|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
173.189.218.254
Since I started this whole shebang with building a 26/26/45 amp in mind, I thought I should go ahead and bread board the 45 before going any further with the 300B. This morning I switched out the 5vdc tranny for another 2.5 and set everything up to try and hit the operating points shown in the the RCA tube manual of plate voltage 275vdc, grid volts -56vdc, plate current 36mA. I didn't need to change anything on the 26's as they were set up for a 45 originally. All the filament trannys are back on AC.
Dividing 56 by 0.036 gave me a starting point for the cathode resistor of 1555 ohms, so I used a 1.5k that was handy and paralleled it with a 47uf cap. Not too surprisingly the measured numbers are pretty close to recommended at plate volts of 272vdc and grid voltage of -56.2vdc, which gives a plate current of 37.5 mA with the 1500 ohm cathode resistor. Close enough to do some listening.
I listened to the one channel with a mono recording for a while and it sounded pretty good, so I decided to do the left speaker right speaker trick again with the 45 and the 91A clone (300B) playing at the same time (one channel of each through one speaker) with a mono recording and just turn one volume control down and one up and then switch after a bit.
Again, it's not entirely apples to apples as the 91A has the magnequest FS030 opts and the 45 bread board has a hammond 125ese. You could definetly hear a diference. At first I thought it was the opt difference, but then I realized that the 45 was sounding cleaner and clearer and a bit more detailed than the 300B; traits that the 45 is famous for. I think I was hearing a difference in the tubes as well.
Suffice it to say that the 45 held it's own even without an expensive opt. Of course I have always felt the 125ese has never received the respect it deserves from the diy community; there is a lot of good sound there for not too much money. Don Garber even offered them as a lower cost option on some of his amps.
I am pleased enough with this amp that I think I will build it instead of the 26/26/300B as the difference between the 26/26/45 and the 91A is greater than the difference between the 91A and the 26/26/300B. The 91A does a pretty good job of utilizing the 300B, so I will just let it.
Next step will be to see if I can re-purpose the old chassis and parts from the psu and front end of my old 6sn7/76 preamp to build the deuce 26/45. The work is just starting!
Edits: 01/19/16 01/19/16 01/19/16 01/19/16 01/19/16 01/19/16 01/19/16 01/19/16 01/19/16 01/19/16 01/19/16 01/19/16Follow Ups:
You build an amp around the 50.
once ... back when... I bought a early maybe 1940's DIY Push Pull type 50's, off ebay . It had a 310A input driving a 45 IT coupled to the 50's ..it didn't come with the 50's, it did have the other tubes and a pair of beautiful Globe Type 81 half-wave rectifiers.
.. I had a pair of 50's to use , so I got it running.....Man was that thing loud, lots of power, a bad volume pot made it hard to control.
Presently I run my 50's in my Universal SET amp. I think they more rich than a 45.....But they both share the same single flat plate design, Not like the 2A3 or 300B..... so there you are !!
Ha
Willie
Tell us more about this universal SET amp of yours! It sounds like just what I need for experimenting. Do you have a schem you would be willing to share?
Edits: 01/22/16
Vinnie , that amp started as VT-52 cap coupled amp. Then it got Electra-Print IT's.
Now it's Directly coupled ,multi-voltage 6.0Amp DC filament supply. A low B+ 325vDC or Hi B+ 450vDC ,
B+ toggle switch (only w/power off). Bias meter with switchable Left or Right Output tube.
It's cathode biased by big watt variable pot and a big watt wire-wound.
I can dial in a wide range of ma.'s for just about any bias point I want.
Test points for Plate and Grid voltage for each output and a Grnd.
So I can run just about any 4 pin DHT around. I even made and adaptor to run a German made triode awhile back.
Lately I've improved my sound system, so it's been fun going back and listening to my amps and my 26 preamp again.
Have fun!
Willie
I actually had a very nice amp that could run multiple output tubes. It as a KC1 > 112A > 45/183/VT-52 and even 50s. I actually liked the 183/483 best. It was a very nice amp. I sold it and kept a 801A but it was a very good amp and I just could not justify having two amps with a lot of money tied up in them. Seemed like a waste.
Yeah GEO
I remember seeing pictures of that amp and you speaking of how good it sound. Yes it was a beautiful piece.... Did you build it ? ...... Whoever ..... nice work !
Willie
Burgess built it. It was really a very good amp. I probably like the 801A amp better but they were both very good. I miss it sometimes. The 183/483s sounded best.
Yes 182/183/482/483's are really nice too, maybe more punchy or punchiness !! .... love them too!
Over the last 15yrs I've often thought of selling that amp, but it just gives me too much pleasure hearing different DHT's.
Willie
Yes 182/183/482/483's are really nice too, maybe more punchy or punchiness !! .... love them too!
Over the last 15yrs I've often thought of selling that amp, but it just gives me too much pleasure hearing different DHT's.
Willie
The thing is it could play multiple tubes. I would have sold the other one.
I kept the one I liked best. Send an email. I may have schematic for the flexible amp. It was excellent.
I would be happy to, but you don't acept unsolicited email. My address is vince@vrhea.com if you find the schematic. I would appreciate it.
ok I changed it.
nt
And why would I want to do that?
I haven't heard a 50 but from what people say, if a 45 is "magic" a 50 is "super magic".
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
For 25 years of my experience, the SET aficionados doted first on the 300B, then on the 2A3 and type 45. For more power there were other choices, but only recently have I ever heard of the type 50 used as an output in an SET. I've heard a pair of such amplifiers, and they really are excellent sounding. But why was that tube seemingly overlooked for so long? Rarity?
Thanks.
!
The Mind has No Firewall~ U.S. Army War College.
JC Morrison wrote a 50 SE article for Sound Practices in 1994. He mentioned the difficulty in obtaining 50s even then and had a conversion for using 845 instead.
Wasn't that just for building the "dinosaur" amp? I don't think he meant you could use the 845 in other applications as well.
Limited circuit choice with NOS type 50 with 10k max grid resistance. EML makes a type 50 that overcomes this limitation. Not as readily available NOS and expensive.
Thanks. That probably explains it.
IT coupled
Hello,
Do you have a schematic or link to share? If not how about some pics of your amp.
Regards,
David
From what I saw on Ebay they are few and far between as well, with a price to go with that. I think I had better stay with my 45's as I already have a good stock of those. Wouldn't mind hearing one of the 50's though. Actually, it's probably better that I don't as I am happy in my ignorance.
Edits: 01/20/16 01/21/16
.
Hopefully at a better price. I have not been able to find anything so far, only older ones on the Bay, and they are too high too.
nt
Vinnie,
I am SO happy you are going Type 45 instead of the 300B !! The Type 45 is such a nice tube, and its easy to drive.
I use an inexpensive output trannie on my 45 amp, and I find OTHER things in the circuit FAR more important than any "expensive" output trannie.
Things such as power supply design, chokes under ten Ohms DCR, and Caps at 50 uF maximum, along with GOOD internal wiring will SMOKE any differences between the most expensive output trannie, and a budget one. No contest ! My mid-2015 Type 45 amp proves this to me rather handily. In the end, we all listen to a modulated power supply. How good is YOURS ??
Have fun listening.
Jeff Medwin
I'm building a 4P1L SE amp for a friend - almost the same bias point, 36mA at 250v but in this case it's filament bias. He's giving me a 125FSE to try out. Input section is 4P1L with Hammond 126B as plate choke and Teflon 0.1 FT-3 coupling cap. Very similar to my home amp which has a Lundahl LL1682 as OPT. 5K into 5 ohms. You might consider that as an upgrade - perfect for a 45. Or the LL1663, 5K into 8 ohms.
I will have to check the pricing. Thanks for the tip.
Another low cost option is the Edcor GXSE line. Don't be fooled by the 40 Hz. LF limit. That's for full power. For #45s, the 10 W. models surely are sufficient.
Eli D.
Thanks Eli. Have you ever done listening comparisons between these and the 125ese's?
I can't say anything from direct experience. However, if I was a betting man, my money would be on Edcor.
Eli D.
Guess I should give them a try as they are less expensive than the 125ese's as well.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: