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GRAAF GM 200

166.249.101.108
Posted on January 31, 2012 at 19:56:37
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009






Hello to all, I have just purchased a Graaf GM 200, was wondering if anyone here has any experience or advice, like bias voltage settings, and also does anyone know if the pl500, pl504 and 27gb5 are all the same tube?
Been awhile since I have posted here, been busy at work, I have a set of Fourier Panthere's that have been working nicely for the last year, also have 3 sets of NYAL OTL 3's 2 sets are performing flawlessly and the last set I am going to do a frame off restoration.
My last purchase befor the Graaf was a 6336 22 wpc otl made by R.L.Merz
I really like it as well, for 22 watts it is quite impressive.
Enough about me,
I will gladly pay for any help or info provided, ie schematic diagram and alignment process...
OTL's RULE !!!

 

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RE: GRAAF GM 200, posted on January 31, 2012 at 23:04:01
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 Sorry I don't know much about Graaf, but perhaps some of our European contributors can help.
That's quite a collection of OTLs. What speakers do you use? I am as much a devotee of ESLs as I am of OTLs. The two go together like...... OTLs and ESLs. Just bought a pair of Beveridge 2SW speakers with their direct-drive OTL amplifiers.

I am surprised to see those output tubes. I heretofore thought Graaf used the 6C33C.

 

RE: GRAAF GM 200, posted on January 31, 2012 at 23:54:30
6AS7_6SN7
 Here you can find the schematic of the GM20.

http://www.audiodesignguide.com/otl/graaf20.gif

Best Regards
Luca

 

RE: GRAAF GM 200, posted on February 1, 2012 at 07:20:35
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009









I'm using a set of Klipsch Khorns in my main system, they are from 59' they are 16ohm and use the wood mid horn as opposed to the later metal version, they sound very nice, with the newest amp in dining room, the Merz 6336 stereo otl I am running Von Schweikert vr-4's, I have a set of
vandersteen 5's I intend to try in the main system along with a set of magnepan 1.6's that have custom crossovers and bubinga wood stand and trim, the pic below shows the dining room system with a set of Decware fullrange speakers, the NFX, really nice but limited in the bottom.

 

FWIW the GRAAF GM 200 and the GM 20 are quite different., posted on February 1, 2012 at 12:26:40
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
 Its been a long time since I've seen the schematic, but if I recall right, the GM 20 uses the output section power supplies to also operate the input section; I don't *think* the GM200 uses that same technique.

 

RE: FWIW the GRAAF GM 200 and the GM 20 are quite different., posted on February 1, 2012 at 13:18:26
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 I briefly looked at the schematic that Luca provided, and I do believe I saw a separate supply for the front end of the GM20. But the output tubes shown on the GM20 schematic are unlabeled triodes, which I believe to have been 6C33Cs. Whereas the GM200 is using something else for outputs that appear to be pentodes. In a circlotron, which the GM20 is, could one run the front end off one or both of the output supplies, successfully? I would not have thought so.

 

RE: FWIW the GRAAF GM 200 and the GM 20 are quite different., posted on February 1, 2012 at 14:06:04
R


 
Hi Ralph, I feel quite honored to get a reply from you, years ago a friend of mine in Oklahoma city built a set of the Novacron kits you used to sell , those were the best amps I had ever heard, I had planned to build a set of the 60's in kit form, I was married at the time and moony was tight, I swore some day I too would have a set of Atma-Sphere OTL amps. Now I have 5 sets of otl mono blocks, 3 sets of nyal otl3's, Fourier panthere's and a set of Trancendents that use the 6c33c's, R.L. Merz 6336 stereo and now this GRAFF GM200... I promise this, my next otl's will be Atma-Sphere's , not because the others have been a bad experience, quite the contrary, I love them all and have no intentions of letting any of them go. The OTL-3's are my favorite. I just hope I can get this Graaf up and going, if it sounds half as good as it looks it will be a great amp. The reviews I have read have been all positive.
Once again I thank you for your correspondence and thanks to Lew too for his input as well.
I'm away and won't get to see the Graff amp til next month, I purchased 70 output tubes today, all matching date code Sylvania's for $5 ea. Plus shipping, that was a good deal, enough to load it up 2 times plus some spares. Can't wait to check it out...

 

RE: FWIW the GRAAF GM 200 and the GM 20 are quite different., posted on February 1, 2012 at 14:40:51
Banat
 Hi Lew !

From my attached link you can download more accurate schematic of Graff GM 20 power Amp .

There is obviously that input differencial stage (6922 tube) is AC bootstraped to output Circlotron power bridge , formed around of two 6c33c-b power tube .
Input differencial stage (6922 tube) DC B+ feed is sourced from the same output power two floating B1/B2+ power supply .
Two separate DC bipolar supply sources is designed to be B+ source for two drivers EF184 tubes (+297V ), differencialy conected .
And - 250 V source is designed to be the B- supply for both differencial input and driver stage , and in the same time is source for negative B- Bias supply for output Circlotron power stage .
It is my personal opinion that model Graff GM200 is designed in simmilar way , more or less .
Best Regards !

 

The GM20 has some similarity to the Cecil Hall patent.nt, posted on February 1, 2012 at 14:49:58
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
 -

 

RE: FWIW the GRAAF GM 200 and the GM 20 are quite different., posted on February 1, 2012 at 15:04:17
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 Yes, I see now that that separate supply at the bottom of the schematic is merely the bias supply for the grids of the output tubes. Interesting.

 

RE: The GM20 has some similarity to the Cecil Hall patent.nt, posted on February 1, 2012 at 16:06:13
Banat
 Yes I agree with You !

More time I spend analyzing this Graff GM20 OTL Circlotron circuit design I find him more and more that is very,very good designed !, and is designed in very elegant way to .
Think beacose that differencial Input gain stage is bootstrapped with Output Circlotron power stage the whole amp circuit is internally very dynamically coupled , and some specific resulting Amp sonic signature exist there for sure to .

Best Regards !

 

RE: GRAAF GM 200, posted on February 1, 2012 at 18:33:47
drwkng
Manufacturer

Posts: 54
Joined: March 17, 2006
 GM200 and GM20 is completely different. there is no GM200 schematic available in the net as far as i know.

 

RE: GRAAF GM 200, posted on February 1, 2012 at 18:39:38
drwkng
Manufacturer

Posts: 54
Joined: March 17, 2006
 one more thing, there are a few versions of GM200.

 

RE: GRAAF GM 200, posted on February 1, 2012 at 19:56:42
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 Thanks for the info, I will try to remain optomistic about the whereabouts of a schematic, I guess worst case scenario the Graaf will make a absolutely beautiful boat anchor...
Went down the same road on the Fourier Panthere's, although I never did surface a schematic for them they are functioning without issues... knock on wood... lol
Bryan

 

RE: FWIW the GRAAF GM 200 and the GM 20 are quite different., posted on February 2, 2012 at 19:26:30
airheadair
Audiophile

Posts: 393
Location: California
Joined: October 18, 2010
 I can't help but wonder what speakers you are using with your OTL3's. As I have written before,
I also have a pair of these driving Stax F83's, (with subwoofers by Roger Modjeski) and I think
the sound is stunning. But I don't listen to other stuff any more at all.

 

RE: FWIW the GRAAF GM 200 and the GM 20 are quite different., posted on February 3, 2012 at 05:58:40
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 The OTL-3's were most recently running a pair of 1959 Klipsch khorns, 16ohm, they are a fantastic match, when corresponding with Ted Hammond he said that they were near perfect impedance for the otl-3, stating that the amplifier was designed to have full output into a 25 ohm load.
I have also a pair of Von Schweikert vr-4's they are truely full range, flat to 20 hz on the bottom, they are my favorite speaker with the Futterman, I'm using them in a dining room system now being drivin with a 22wpc merz otl.

 

RE: GRAAF GM 200, posted on February 3, 2012 at 06:32:50
tyu
Audiophile

Posts: 963
Joined: April 19, 2011
 Thanks for the post an the pic...

 

RE: GRAAF GM 200, posted on February 3, 2012 at 18:31:11
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 i-phone video of last time I was home, had just put the Fourier's in the system running the old klipschorns, nice and tight!!!
lol, amature mastering and video.
oh well many members have asked what speakers I am using so here it is til I try something else.

http://www.youtube.com/watch?v=rEWBB4mFBdM&feature=mfu_in_order&list=UL

 

RE: GRAAF GM 200, posted on February 3, 2012 at 18:35:31
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 addendum

 

RE: GRAAF GM 200, posted on February 3, 2012 at 20:47:09
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 a look at my hi-fi repair shop, try to spend as much time there as I can when I'm home.

 

RE: GRAAF GM 200, posted on February 4, 2012 at 07:57:24
lone gunmen


 
search 'fourier capacitors' in the archives

 

RE: GRAAF GM 200, posted on February 26, 2012 at 14:58:22
Mark S Allen
Audiophile

Posts: 9
Joined: September 1, 2001













I own a Graaf GM200 and it is both an absolutely stunning sounding and looking amp. Just bought a second one (along with a matching GM 13.5B II preamp and GM70 phono preamp - a bit like finding hen's teeth to locate these two) so that I can bi-amp a pair of Wilson Benesch Bishop speakers with them. As you can see, the bug has bitten very hard with this one...

As far as the tubes that can be used with this amp, either the PL504 or the 27GB5 will work (I've successfully used both). The PL500 has the same characteristics except for anode dissipation - 12W max for the PL500 rather than 16W for the two mentioned.

http://tdsl.duncanamps.com/pdf/pl504.pdf
http://tdsl.duncanamps.com/pdf/pl500.pdf

An important point to make about the tubes - all PL504/27GB5 tubes are definitely not equal. This amp will make you tear your hair out if you don't use QUALITY tubes - they will blow time and again, each time requiring you to open up the amp to unsolder and replace a blown 1 Ohm resistor under the faulty tube. 'Quality tubes' means using either tubes made in Europe or Japan.

There are also quite a variety of PL504/27GB5 tube designs (I have come across at least 6 or 7) and the tubes used should be well matched so they should all be of the same design (not necessarily same manufacturer, as the same manufacturer sometimes uses different designs and vice versa). Fortunately the Graaf factory will be able to supply you with a matched set and can service the amp for you - just remember that they are in Italy and life seems to work at a pace there that is about 1/8 of that in the US... I also have a substantial collection of these tubes, some with the required 32+ of the same design, others with less, so happy to discuss tube swapping with interested GM200 owners.

The literature accompanying the amp specifies setting a bias current on each channel equivalent to a voltage measured between the channel's test point and ground of 75mV but the factory now recommends that this be reduced to 65mV to extend tube life and to allow for slightly higher mismatch between tubes. This obviously also reduces the amount of power that the amp delivers in pure class A mode before it transitions to AB.

The offset voltage on each channel should be reduced to as close to 0mV as possible between the + and - speaker posts (less than 2mV is recommended). The amp has a circuit that constantly measures this offset voltage and will switch the amp off if it goes out of spec to protect the speakers.

When replacing the tubes I personally turn the bias pots completely down so that the current through the tubes is 0 (bias voltage is 0). Note here that the left and right channel bias pots turn in different directions (clockwise and anti-clockwise) to get down to 0 - I have a note somewhere that tells me which direction for which channel but I am sitting in London while writing this, so don't have this with me. I slowly turn the pot the appropriate direction until the bias current starts to creep up and then check the offset voltage and adjust the offset pot if necessary to bring this down to 0. I then turn up the bias further until 65mV is reached, making sure along the way that the offset stays at 0 (or close to). I then check the voltage across the anode resistor on each tube to check how well they are matched. They should all read around 15.5mV plus or minus 2.5mV. Any outside this range should be replaced (this can usually be done without resetting bias to 0 if not too many are way out). Bias is then readjusted, offset voltage readjusted, and the anode currents checked again. Note that the anode current in the front 8 tubes on each channel is slightly higher than the anode current on the rear 8 tubes. Someone technical on this forum may be able to tell me why Mr. Mariani has designed the amp this way - I am guessing so that tubes with higher anode current readings can be placed in the back group and those with lower readings can be placed in the front group to get the closest possible match of current through all tubes, but this is just a guess and I might well be wrong.

I have attached a picture on the amp. I also have some schematics that give some but not all details - these are for one of the two potted blocks in each channel of the amp - the single-ended/balanced input module (there is another potted module on the driver board (a coupling capacitor and resistor network)). I have included a circuit that will replace the input block with a passive single-ended input (does away with one input tube).

I do have the service manual that gives details of the full circuit, wiring diagram to change line input voltage to 220V/110V/etc. Feel free to contact me if you need this - haven't worked out a way to upload this .PDF file.

 

RE: GRAAF GM 200, posted on February 28, 2012 at 05:21:35
tyu
Audiophile

Posts: 963
Joined: April 19, 2011
 Thanks for all the INFO.....I would like to see the schematics if an when you can post..Any info on OTLs you have helps

 

RE: GRAAF GM 200, posted on September 23, 2012 at 12:33:59
ideiaprint
Audiophile

Posts: 1
Joined: June 30, 2012
 Hello to Mark S Allen and all.
I must ask your comprehention and tolerance with my english. It is not my mother language.
I read with much interest your long explanation on tuning up the Graaf 200 OTL.
I have one too. But the matching procedure is very long and very time consuming. I already did Graaf method but I canīt match well.
I was working with 65mA on Bias, but now have lowered a little bit further to 50m, just for precaution.
I have an Hickock 600 tube tester that tests the 27GB5 /PL504.
Most of the spare valves I have reads between 4000 & 5000 and try organise them like that in the amp, but when I try Graaf matching procedure direct in the amplifier ( those 15,5 & 17,5mV) everything get wrong. Is just like this proceedure contradicts the Hickock.
Most of the 4000 valves read 19-20mV and some 5000 reads 8~10mV. It crazy, and I donīt understand why.
Can you help Mark? It seems you have a lot of experience in this amp. I have other OTL amps that sounds much better. Perhaps I am doing something wrong. My speakers are Quad ELS 57 and YAMAHA NS1000M.

 

RE: GRAAF GM 200, posted on October 12, 2012 at 23:29:19
piggo
Audiophile

Posts: 1
Joined: October 12, 2012
 Hello Mark,
thank you very much for the useful informations you posted. I just bought a used GM200 and I would like to get the service manual.
Is it possible for you to email me the pdf?
Thanks in advance and best regards.

 

RE: GRAAF GM 200, posted on November 26, 2012 at 12:37:05
Mark S Allen
Audiophile

Posts: 9
Joined: September 1, 2001
 I would recommend that you match tubes by:
1) Doing a basic test with a tube tester to make sure that the tube is in working condition
2)Putting the tube into the amp itself at a set tube position in the amp when the amp has been set up at the correct bias and then measuring the voltage across the anode resistor of the new tube when the amp is on. Write down the voltage across the anode resistor for each tested tube and this can then be used to grade your tubes so that you can select similar tubes that have been tested under operational conditions.
If you put in a new tube in every time you switch on the amp to listen to it, and you listen once a day, you will have tested 30 tubes by the end of the month. I have had tubes measure almost 0 V across the anode resistor (i.e. tube is virtually not operating) and the amp works quite happily with the remaining 15 tubes in the channel spreading the load and showing 1mV extra across their anode resistor. The amp will actually happily work with one of the tubes being blown (red LED showing next to the tube).

While on this subject, I had the opportunity to visit the Graaf factory in Modena about a year ago and see Mr. Mariani fix a GM 200. Not something I would recommend but he happily disconnected the anode clip on a PL504 tube, unplugged the tube, plugged in a new tube and reconnected the anode clip, all WHILE THE AMP WAS ON without any problems (no speakers connected). As I believe there is about 150V on those anodes there is NO WAY I would do the same, but he certainly did, being careful not to touch anything else (comes with 40+ years of playing with tube amps, I suppose :-) ).

 

RE: GRAAF GM 200, posted on February 6, 2013 at 00:28:55
johntyblue


 
they run very hot ,take base plate off and sit it up on blocks to encourage airflow - consider under-volted low noise computer fans
if not ventilated soldering etc can start to deteriorate

regards

jt

 

RE: GRAAF GM 200, posted on April 7, 2013 at 04:22:58
berni
Audiophile

Posts: 184
Joined: May 30, 2011
I also found a nice gm200 checked personaly by mr.Mariani himself. The PL504 tubes used, by his words one of the best and rare are RCA.
What only makes me think is that the unit has only the unbalanced input. I always thought it was balanced only??
I hope it will be able to drive my Magnepan 20.1 speakers, I know that this is not the best match, if it will be to hard on the tubes, I can still use my MC2 mc1250 amp on the bass and the Graaf on mid/ high. Will report how it turns out.

 

RE: GRAAF GM 200, posted on April 7, 2013 at 06:16:21
berni
Audiophile

Posts: 184
Joined: May 30, 2011


Here some photos of the beast.

 

RE: GRAAF GM 200, posted on April 7, 2013 at 13:45:52
berni
Audiophile

Posts: 184
Joined: May 30, 2011



Another one with the RCA logo...

 

RE: GRAAF GM 200, posted on April 9, 2013 at 19:53:47
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 That's nice, glad you are enjoying your amp, mine is still sitting in the box beneath my workbench, where it will probably rest for a long time, I was hoping to get it up and going but too many other projects are in front of it. I have a box of over 80 nos sylvania's for it too.
Maybe someday...

 

RE: GRAAF GM 200, posted on April 9, 2013 at 22:46:08
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 Where did you get the pl504 in large qnt?
I heard from Mariani that they should be matched in 4 octets and that the Japan made were the best(different brands but it was always the same factory).
I first must set it up for proper voltage,but I have no manual only some pictures of the wiring and a code for the wires how it is done.

 

RE: GRAAF GM 200, posted on April 10, 2013 at 10:30:35
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 I have heard from Mariani (GRaaf owner) that the 32 pl504 should be matched in octets!!! So maybe 80 tubes is not enough to get it right even for one side....
He has a very strickt policy on that, and I think other that "knew" better just gave a bad reputation on the realibility of this otl-s. And this is not fair.

 

RE: GRAAF GM 200, posted on April 11, 2013 at 05:40:49
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 I have a copy of the entire manual on my home computer, I'm away on
business for a few more weeks, but I can send it thru e- mail when I
return.
About the tube matching, from my personal experience I use an amplitrex
tester to test all tubes for plate and mutual conductance, just last year I
tested 50 6lf6's for my futtermans, they use 6 per amp, I ended up with 7
matched sets from the 50 tubes, 8 tubes were either too high or too low to
fit in to the sets.
I installed the worst of the sets into a pair of amps, aligned set bias and
balance and let them work together for 200 hours before I listened to music
or turned them off, that's 8 days. I then listened to them for a few months
about another 200 hours then retested the tubes, they were matched to
within 1 milliamp of each other when retested, much tighter than when I put
them into the amps.
The way the tubes work together in circuit seems to dial them in tighter
just by being in circuit.
Therefore I feel 80 tubes for the Graaf should yield 2 complete tightly
matched sets for the amp. 32+32.

 

RE: GRAAF GM 200, posted on April 11, 2013 at 05:58:12
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 That would be great if you could send me the manual.
here my adress info@keber.si
Thanks in advance.

 

RE: GRAAF GM 200, posted on May 15, 2013 at 12:19:23
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 Hi, I would really love t get this manuals if possible. :)

 

RE: GRAAF GM 200, posted on May 15, 2013 at 12:19:47
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 Hi, I would really love to gett this manuals if possible. :)

 

RE: GRAAF GM 200, posted on May 24, 2013 at 08:24:50
MIk-


 
lot of tubes,thanks for the pic.

 

RE: GRAAF GM 200, posted on May 27, 2013 at 02:49:31
berni
Audiophile

Posts: 184
Joined: May 30, 2011



I had the rare opportunity to see and test the new GRAAF GM400 before the launch in summer or autumn this year!!
All I can say is that it is awesome, the first transistor with a human OTL like sound. As great as all of the Mariani concepts.

 

RE: GRAAF GM 200, posted on October 22, 2013 at 19:30:21
i.browne@optusnet.com.au
Audiophile

Posts: 2
Location: Victoria
Joined: October 22, 2013
 I also have owned a Graaf Gm 200 and have been very happy with it. It seems as though you have done quite bit of experimenting with the PL504 out put tubes. With your experience have you found any sound difference between different manufactures of the PL504 tube. Also,for sound quality does the set of tubes need to be from the same manufacturer. My amp, which I have had for last ten years, has at the moment a number of different brans of tubes. These included National Electrics CVC Chember and many unbranded. Can biasing the amp overcome any difference with the tubes.I have found a set of 32 PL504 from Valvo made by Mullard. Have you had any expierance with these tubes. Appreciate your advice.
Cheers Ian

 

RE: GRAAF GM 200, posted on October 29, 2013 at 12:06:43
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 Mr.Mariani said that it is very important that the t ubes used are very tight together and of same characteristics- meaning one type. I have a second set of Telefunken and he personaly said that I should not mix them with other made by Philips or others, because they behave different when high demands...
By his words the RCA made in Japan are one of his favorites.... But I could not find any ...

 

RE: GRAAF GM 200, posted on October 29, 2013 at 14:24:42
i.browne@optusnet.com.au
Audiophile

Posts: 2
Location: Victoria
Joined: October 22, 2013
 Does that mean that tubes can be different brands but need to be physically
the same. Also when matching tubes does the whole set of 32 need to be the same value.

 

RE: GRAAF GM 200, posted on October 30, 2013 at 01:29:13
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 They should be the same means either same producer and same type or different labels but same producer and type. Mr. Mariani said that this is of great importance, so the tubes perform at every level the same.
Also the tubes should be matched in octets. You have two octets on the left and two on the right side. How exactly he measures them I don't know. He has them running for a while then measuring again.
My set of Telefunken is waiting for teh day to come at his home.
You can still contact him on this email:
info@graaf.it

They are again in bussines. :)

 

RE: GRAAF GM 200, posted on January 7, 2015 at 12:31:00
LuisVinhas
Audiophile

Posts: 3
Joined: January 7, 2015
 Hi,

I just purchased a GM200 and agree that it is a superb amplifier.

I've read that one or two of you have a copy. If willing to share it freely, much appreciated. I am currently in Europe on a work assignment and am concerned that technical assistance may be an issue particularly when I return to the US, so would ideally like to have a copy of the service manual.

I will be soon looking into buying a new set of tubes so will be keeping an eye for alternatives on that front. Regards.

 

RE: GRAAF GM 200, posted on January 9, 2015 at 09:41:56
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 Congrats.
Which type is it ? The unbalanced or the balanced one?
I can send you the service manual if you send me your email adress, but not before Monday.
But the manual has little info on how to setup or bias the unit...
Mine was tested and properly tuned by Mariani himself..
Regards
Bernard

 

RE: GRAAF GM 200, posted on January 10, 2015 at 06:08:54
LuisVinhas
Audiophile

Posts: 3
Joined: January 7, 2015
 Thanks Bernard. Appreciated. My GM200 is balanced. It actually came with a manual but a very terse one on how to tune up the amp. I was hoping that there would be a more thorough service manual with diagrams and further specifics on adjusting the amp.. At any rate, happy to take a look at the manual you have (my email is luisavcatao at gmail.com). The previous owner kindly indicated to me the recommended bias and am familiar with both DC offset and bias setting from a previous amp, so guess I can get by with those basics for now.

I am indeed planning to take the amp at some point for some tune up by Mr. Mariani but doubt I will have time for that until the Spring. At the moment what seems more pressing is the decision as to whether to get a tube tester which tests PL504s since I basically have no replacement power tubes, so should one or more blow up I can't operate the amp. Any reference to not-so-expensive tube testers that do a decent job at testing the PL504s are welcome -- I hear great things about the Amplitrex tester but that's beyond my price range at least for now. Also hear good things about the Hickok TV7 and the B&K Dynascan 667 but haven't been able to confirm whether they test the PL504s. Regards, Luis

 

RE: GRAAF GM 200, posted on January 17, 2015 at 08:54:06
LuisVinhas
Audiophile

Posts: 3
Joined: January 7, 2015
 Wonder whether someone has used a PL504 brand RFT and/or another called Tungsram in the Graaf GM200? Regards

 

finally determined a use for this amplifier..., posted on February 17, 2015 at 19:30:51
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 Looks like my father who actually has no interest in OTL amplifiers has shed light on the perfect use for this beast. We have talked for years about putting our funds together and purchasing a small fishing boat, probably 16 to 18' in length, flat bottom with a small maybe 20 horse mercury motor. The Graff he says will work perfect for a nice anchor to hold us on the points and flats that he says we will be fishing, he did note that the tubes would have to be removed to provide the best drop and hold, he also suggested the tubes would work nicely for bobbers, and crankbaits for different depths, topwater, midrunners and deepdivers all with simple adjustments to the size of the bill at the head of the Lure/Tube.
Hard to believe that my dad came up with this fantastic idea, harder to believe is that I agree wholeheartedly!!!

OTL's Rule!!!!
the waters...
lol














 

RE: finally determined a use for this amplifier..., posted on February 21, 2015 at 12:53:05
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 Where is this anger coming from ? :)

 

RE: finally determined a use for this amplifier..., posted on February 22, 2015 at 19:00:01
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 No anger here, just having a little fun that's all.

 

RE: finally determined a use for this amplifier..., posted on February 23, 2015 at 13:58:58
berni
Audiophile

Posts: 184
Joined: May 30, 2011
 ;)

 

RE: GRAAF GM 200, posted on August 12, 2015 at 08:28:24
Frederichabert@hotmail.com
Audiophile

Posts: 3
Joined: August 11, 2015



Hello Mark,
I need a little of your knowledge about Graaf GM200 if it's possible, I find, on power board a little part who became very Hot( not very far of R28 , a name part on board is " MV1" ), I dont find on schematic, this reference neither his value..?

I supose this part is CTP but could you give me value and reference of this MV1 part, and perhaps you could send me better schematic information with technical diagram.

I tried to contact info@graaf.it but nobody answer even by phone...unfortunately.
Could you help me in checking on your GM200's?
(I tried to upload a pics of the part but that's don't work...if you have personal email address i can send you the pics of this piece)

Many Thanks
Best & Kind regards
Fred

 

RE: GRAAF GM 200, posted on August 13, 2015 at 01:37:36
Frederichabert@hotmail.com
Audiophile

Posts: 3
Joined: August 11, 2015



Hello Bryan,
I need a little of your knowledge about Graaf GM200 to try to fix mine!

I find, on power board a little part who became very Hot( not very far of R28 , a name part on board is " MV1" ), I dont find on schematic, this reference neither his value..?

I supose this part is CTP but could you give me value and reference of this MV1 part, and perhaps you could send me better schematic information with technical diagram as you purpose kindly in your message..?

I tried to contact info@graaf.it but nobody answer even by phone...unfortunately.
Could you help me in checking on your GM200's or schematic/technical data sheet?


Many Thanks for your help
Apologize me to disturb you but i don't have any other way as Graaf & Mr Marianni doesn't reply anymore...
Best & Kind regards
Fred

 

RE: GRAAF GM 200, posted on August 14, 2015 at 22:05:29
Mark S Allen
Audiophile

Posts: 9
Joined: September 1, 2001
 I am guessing that what you are talking about is what is called an MOV (Metal Oxide Varistor). It is a component that acts like a high-value resistor until a certain voltage across it is reached, at which point it becomes a low-value resistor. Until the voltage across it rises to the cutoff point, it will dissipate quite a bit of power and it is normal for it to get very hot. Once the cutoff point has been reached (when it becomes a low value resistor) the dissipation will be significantly reduced and it should cool down significantly.

It is usually used to prevent current surges in an amplifier when the power supply is ramping up to its working voltage. Once the PS working voltage is reached it essentially switches itself out of the circuit as its resistance is reduced. I would not be too concerned about this component getting hot unless there is some other fault present or it is looking like it is burnt out.

Here is an article on them:

http://www.cliftonlaboratories.com/metal_oxide_varistor_%28mov%29.htm

Of more concern in the GM200 are some pretty large wire-wound resistors in the power supply that are about 2-3" long. There are two of them, almost immediately after the rectifier bridges, that get EXTREMELY hot if there is a fault in the amplifier (normally they are not used but plugging the amp into an incorrect line voltage e.g. 220V when the amp is set for 110V, would be such a case or if there is a short in a power tube). As they were mounted directly onto the PCB in early amps, there have been rare occasions where they have caused the PC board on some GM200 amps to catch fire! The solution to this (that can be seen on the later constructed GM200s) is that they are installed with long leads that lift them off the board by about 1.5-2" so that they can dissipate the heat properly and not heat up the PCB. If you find your amp has these two resistors mounted directly on the PCB you should probably install two exact replacement resistors that are mounted above the board on their leads.

Hope this helps...

Kind regards,
Mark.

 

RE: GRAAF GM 200, posted on August 14, 2015 at 22:15:55
Mark S Allen
Audiophile

Posts: 9
Joined: September 1, 2001
 Johnty,

I have to disagree with this... the GM200, when the bias is set correctly, does not run particularly hot, even with all of those tubes. I did some temperature measurements directly on the power tubes themselves and they were around 60-65 degrees Celsius, which is really not that hot for a 200W power amp - even solid state amps of this power will start to get to those figures.

The major determining factor in heat dissipation is the bias setting. Graff originally specified that they get set to quite a high bias current to wring the utmost audio performance out of them, using highly matched power tubes. Graff has since recommended that the bias current be reduced quite a bit for two reasons:
1) it makes very little difference to the sound of these amps
2) 16 x 2 sets of very closely matched power tubes are pretty difficult to get hold of these days

 

RE: GRAAF GM 200, posted on August 14, 2015 at 22:20:46
Mark S Allen
Audiophile

Posts: 9
Joined: September 1, 2001
 RCA tubes, especially those made in Japan, followed by Europe, are highly recommended if you can find them.

 

RE: GRAAF GM 200, posted on August 14, 2015 at 22:28:40
Mark S Allen
Audiophile

Posts: 9
Joined: September 1, 2001
 Unfortunately choosing tubes from one manufacturer (e.g. RCA or Mullard) does not always work, unless they are made by the same factory, as there are multiple physical designs of the PL504 tubes that are sold by a single manufacturer. As an example, have a look at some Mullard tubes and you will see that those made in the UK have a getter (silver ring at the top of the tube) that is oriented vertically, while those made in Holland are horizontal.

You want to try and get tubes from the same manufacturer and manufactured in the same way (e.g. all Japanese manufactured RCAs are made the same way, as far as I know).

 

RE: GRAAF GM 200 "My Precious!", posted on August 16, 2015 at 04:27:19
Frederichabert@hotmail.com
Audiophile

Posts: 3
Joined: August 11, 2015
 Hello Mark,
Many thanks for your explanation,
that's really nice to find people like you available to share their passion & knowledge to help us.

My Graaf GM200 model (is Balanced) appear to be the second version with the right resistance modification on the power supply...
(with the trick to lift them off the board to dissipate the heat away from PCB) that is pretty a Good News! the Latest revision.

Manifestly the 4xEFL200 failed & need to be change to test as well the tension...
I'm gonna change, as you advice me, these two resistors next to rectifier bridge for exact replacement before change this MOV.(thermistance) to check what happens?

I still investigate and let you know when it's done in hoping there will be no other amp fault or problematic issue.
(i ever changed many 1ohm blown resistor under the PL504... i changed the 32 Output tubes for same ones to keep them matching together)
Anyway, if you know where it's possible to find an other 32xPL504 Good quality set, i Still interested!
(cause in France it's complicate to find large matched quantities from Good Brand & same construction of these old TSF tubes!)

Mr Marianni is unreachable since 2 years, i tried by many way to contact him, even since the launch of the new GM400, maybe already out of business..?

I saw you had 2 xGM200, i Dream to find an other one to get a pair !
did you use yours in Bi amping/Bi wiring or have you bridged them?
i would like, i don't know if it's possible..?
Bridge mine as Mono for 400watts (with 2 pair of output binding post to Bi wire my MBL speakers..?) to keep the power in 4ohms as final Goal.

Did you have any idea to do that without affect the reliability or it is complicate Job from your point of view?

Could you, if you have, send me some Schematic diagram with technical data sheet & value (ALL you have about this Beloved Graaf!),
cause the original Graaf user manual than i have is really Poor in instructions!

Best & Kind Regards
Friendly Yours
Fred

PS= I dream to test The Destiny VZN350 Joule electra based on 6C33C (as the lamented TENOR 75) and the Atmasphere MA2 but there is quasi none in europe...have you ever heard the Silvaweld OTL 200 base on 6C19 tubes..?
Did you know SI audio ? an italian OTL manufacturer & the Fedelta hifi review owner
http://www.siaudio.it/index.php?option=com_content&view=category&layout=blog&id=76&Itemid=127

 

RE: GRAAF GM 200 "My Precious!", posted on August 16, 2015 at 05:18:05
Banat
 Hi Friedrichabert !

Check on this Tubes RS site for PL504 tubes , original EI NIS-NOS tubes for which I personally know that quality is very good ,
I known personally that guy( Dragan Nikolic) who sell those tubes and hi is OK guy , but on the other hand I consider that 17E per PL504 tube is way to hot price , but maybe if you by large number of those tubes the net price can go down significantly .

Best Regards !

 

RE: GRAAF GM 200 "My Precious!", posted on August 20, 2015 at 09:09:44
rhinohifi714
Audiophile

Posts: 174
Location: oklahoma
Joined: June 13, 2009
 here is a good deal on 40 pl504's

http://www.ebay.com/itm/8-x-PL504-Ei-YUGOSLAVIA-BEAM-POWER-TUBE-NOS-NEW-/262000899096?hash=item3d00787418

 

RE: GRAAF GM 200, posted on August 21, 2015 at 07:48:44
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 The best tube tester is the amplifier itself, for the power tubes. If the tube under test is within the limits for voltage across the anode resistor, it's probably "good". That tells you that under the bias conditions prevailing in the amplifier and with the DC voltage provided by the PS, the tube passes an amount of current that is the same or similar to the other tubes. This should be done with all other sockets occupied by "good" tubes, ideally.

 

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