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The 500c and the Mac 1500 are two interesting units.I have six of the 500c and one 800c. The 500c and 800c are all tube units including preamp section while the mac 1500 has a discrete solid state preamp,but the tuner and amplifier stage are tube other than the tuner output stage which has four discrete transistors.
All in all,I much prefer the 1500 as it does everything better IMHO.
Some of the reasons for this is the superior iron,the 12AU7 drivers as opposed to a 12AX7 which are weak by comparison.I say this because on the 500c,there is a slope that develops as you get past 12 o-clock on the volume control and distortion rises dramatically.The 1500 I can take all the way to 4 o-clock on the volume pot and I'm still not clipping and the 1500 is making more power. It also has separate bias pots for the 7591s.
The tuner in the 500c is very good but it also very good in the 1500.What I really love about the 1500 is the fact that it's quiet and that allows you to hear more detail and little nuances that would otherwise over look.
Now keep in the mind that I rebuilt that this unit with new filter caps going up 2.5 times the original values.I also uses Schottkys in the power supply and I did change transistors in the phono section to ones that were more quiet.I changed all coupling caps to k40s and Solen Film and tin foil.Muse caps all thru the bias and emitter circuits.
The main problem with Mac 1500 is the high impedance 10v supply.There is a filter cap that shorts and that will kill the preamp.
Now before you go off on a tangent thinking I'm crazy,I'm working on a circuit for the 500c that will help dramatically..I'm changing the 12AX7 driver to a 7247 or a 6U8a.The feedback also needs tweaking in the 500c because the Sherwood S-8000 runs well with a 12AX7 driving the 7868s but,the iron and feedback are different.When I feel better,I will do more testing on the 500c preamp. Right now tho,this 1500 just gets it in every way.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Follow Ups:
It is interesting to see the love for the McIntosh 1500. The C26 pre which is the basis of the 1500 doesn't get much love.
I've recapped my c26 per Terry Dewick and others on AudioKarma and it is fine (not my favorite pre but is sure is pretty).
looking for some jazz and a little libations - joe strummer
Keep in mind that the preamp of the 1500 is going thru a tube amp and driver stage which helps a lot.Put Schotky diodes and PME-271 paper in wax caps in the audio path and you will really like you C26 much more. The C28 and C32 are much better but,you can do much more to your C26.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Thanks Mike. We might have chatted about these kemet caps in the past.
I'll put them on my next mouser order. I did not change out the coupling caps, only the electrolytics.
looking for some jazz and a little libations - joe strummer
here is a pic
looking for some jazz and a little libations - joe strummer
Edits: 12/03/16
That sure looks nice. Where does the sound fall short for you?
a Fisher 500c and a Mac 1500 in stock form ( i.e., they need work) Is the mac the one to have restored rather than the 500c? Thanks Norm
Norm
I think so absolutely. I'm awe struck by the 1500 with the mods I put in it and the other receiver I find to have really articulate balance as is the HK TA-260.The Mac 1500 just does it right.It doesn't behave like it's compromised like so many receivers are.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 12/02/16
Mike, is the 260 that good? I sadly acquired one after my best friend suddenly passed away. I There isn't a day that goes by that I don't miss him.
Anyway, he had it on ice and was more into the 70's solid state stuff. I remember telling you about it when he got it from some tall guy in San Francisco among other details that escape me and you actually knew the guy he bought it from haha. Small world.
Dan
I got forgot to mention the Sherwood S-8000s are phenomenal as well.Even tho they have a 12AX7 driver,they also have a copper classes chassis.Yes,I like the HK 260 a lot because of the brilliant layout and circuitry,and overall execution.Even the controls are mounted on a separate chassis,away from anything that may cause issues.The iron is hefty as well.The quality of the controls are first rate,at least for the time and still for today.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 12/02/16
Mike, thanks for the reply. I really wanted a 8000 but I didn't pull the trigger when I should have. One was cheapish that needed some work here on craigslist but I was deep into a Fisher 400 at the time.
I'll drag the ta260 out. It's already partially rebuilt. I even have a extra set of output tubes for it.
I just remembered that my grandpa had a 1500 in his den when I was a kid. I would really love to hear one again. How much do they go for?
Thinking about the Fisher. It suffers from the miller effect without a buffer after it's volume pot before the power amp section. I think that is more of the issue than the driver tubes but I could be mistaken.
Dan
Look on Ebay because it can vary.What happened to the one gramps had?
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
It probably got tossed when he passed:(. It was in the early 90's. I recall that he wasn't found of transistor amps probably partly because he could fix a tube setup himself. If I ever run across one and have the extra cash I'd love to pick one up for nestalgia.
The only part of the 1500 is SS is the preamp section but they did it so well that you would never guess it have any solid state components in them.
If you think about it,CD players and DACs have SS output stages,most of them.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Dude, totally. My favorite preamp is a recapped Apt Holman with my tube amps. it just seems to mesh perfectly. As long as the output stage is tube it sounds tube to me.
To be honest I never really cared for the tube preamp with a solid state amp.
I did not think that the 7591 was all that tough to drive. I thought the 12AX7 while weak was up to the job. Many that is why my Scott 222D and Dynaco SCA35 use pentodes for drivers.
Dave
Full pentode mode "finals" are easy enough to drive. It's the "fixed" bias grid to ground resistance limit of the 7591 that's the sticking point. Fisher used 330 Kohm parts that have drifted upwards, over time. The data sheet gives 300 Kohms as max. From the beginning, Fisher was "out on a limb". :> ( Current production 7591s are intolerant of the liberties Fisher took.Mikey is on the right track in thinking 12DW7/7247. AAMOF, Fisher used the 7247 in the X-100. Then, "bean counting" set in. Reduce inventorying costs by stocking "only" 12AX7s. Never mind the fact that the high R P 'X7 triode must work into a high net AC impedance.
I'll upload the relevant X-100 schematic fragment, later today.
Eli D.
Edits: 11/29/16
Eli D.
Schematics start on page 7.
I never owned a Mac 1500, but a few Fisher 400s & 500s. The Fishers are nothing special in stock form. A little muddy IMO. But, after some simple mods & tube upgrades, the Fishers are great & very musical. They sound like a live performance. They are better than a modded Scott 340B too.
They are better than a modded Scott 340B too."
I would love to see the mods you used because I haven't found that to be the case at all. I agree that they are muddy and distorted but I would love to try Danny's mods or ones you used. The 340A I really like and the 340B is good as well with proper upgrades.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Michael, see my post above.
Fisher phono sections are notorious for poor bass extension. Reworking the phono section to use the tweaked RCA setup deals with that and allows the recording O/Ps to have respectable drive level.
Eli D.
Sony, have you ever tried any of the below tweaks that I put a link to in my below post? I still have to order the stuff to fix the riaa curve but the buffer after the volume really was a positive.
Edits: 11/29/16
Rebuilding Mac 1500s now - OK Mike it looks like we are going to have to get you a second job now!!!!
I had two of them in the past and always felt some serious corners were cut to get these to market at a price point. After all they were intended for the "mid level" buyer and not the high end buyers.
It is interesting how you are fixing up some of the ills of that stereo. I always felt it had good bones but as I just mentioned - they were engineered with some serious short cuts and it showed.
There was this zener diode that would always blow - on both of them. Was that the filter cap you were referring too?
LOL
It's funny you say that because I just had two of my auto tech students ask me about the Fisher X202 in the trunk of my old Town Car which I can't lift out right now.Anyway, I have them doing a fuel filter change and FI flush for an exercise and you have to put the car in the air but before you do that,you have to shut off the air suspension in the trunk.That's when they asked me about that old funny looking tube amp that they so were so intrigued with.
I told them I rebuild this stuff and that's when said,does it pay better than teaching.LOL
We have one day a month where I allow them to bring their vehicles in and work on them and I grade the exercise but these two didn't have a car to work on so I let them change the fuel filter and flush the fuel system injectors on my car. Now I don't have to do it.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Mike, you may want to borrow the idea in the below post. It really helped transform my late model 400. I believe most of the Fisher integrated/receiver volume/preamp output sections would benefit from this. I know it's adding silicon but it's worth it in my opinion.http://www.audiokarma.org/forums/index.php?threads/improving-the-fisher-400.511867/page-2#post-6672509
http://www.audiokarma.org/forums/index.php?threads/improving-the-fisher-400.511867/page-3#post-6674188
While you're at it also fix the phono stage's RIAA curve
http://www.audiokarma.org/forums/index.php?threads/the-fisher-phono-preamp-and-riaa.600690/
Edits: 11/28/16 11/29/16 11/29/16 11/30/16 11/30/16
Mike, how have you been? Hope back is healing.
Those trannies have EIA code = 159. I have this as DX Radio Products, Chicago. Never heard of this manufacturer.
Do you know anything about their relationship with McIntosh?
Thanks!
Magnetic Windings of Easton, PA made some of the finest trannies for many vintage HiFi manufacturers.
!
The Mind has No Firewall~ U.S. Army War College.
Is company also know as Essex? That's the EIA info I have for 352.
Anyhow, makes more sense. Entire code = 352529.
529 = 1965, 29th week. So Mike's receiver is an early production model.
Thanks!
8^)
FenderLover, speaking of transformers, is it worth it to replace a large box silver faced Bandmaster's output transformer with a Bassman reproduction?
Edits: 11/29/16
Nope. The Bandmaster (esp the Bandmaster Reverb) has one of the heavier duty OPT, of all dual 6L6GC output Fenders. And it's spec'ed for guitar use. Very clean tone, to super loud.
If you are going to use a bass through the amp --- I'd look for a good bass amp. Like vintage Ampeg Portaflex. Or more modern SVT.
Hmm. the Bandmaster Reverb's transformer seems small for it's class. Much smaller than the Bandmaster non reverb or bassman. Maybe it's a good thing.
It's for guitar. For bass it wouldn't be much fun outside of a practice amp. I have to swap out a mid pot that was changed sometime to 25k and figure out why it thumps when the vibrato is engaged even if it's all the way down. All the electrolytic caps have been swapped and I tried a new LDR.
Unless there is something wrong with that tranny, I'd let it be. Potential buyers will check for trannies made within the time frame of the amp.As for that thump... could be the foot switch. Contacts can get dirty. Sometimes, a little Deoxit fixes the problem.
Edits: 11/29/16
I was using a shorted rca plug to test:(. Just one of those odd issues.
So the amp "thumps" when the RCA shorting jack is in? But, doesn't if you remove this plug?The Vibrato/Tremolo in the Bandmaster, the anode voltage seems to come from point "B." The only filtering prior to this point is the choke (which is prolly ok) and the first filter stage (series 70mfd caps).
Did you change the leveling 220k-ohm resistors, in this first stage? May have some imbalance between those two caps. Not enough filtering for the VIBRATO portion?
I like using 220k-ohm 2-watt metal oxide or 5-watt wire-wound Mills.
Edits: 11/29/16 12/01/16
Thank you for the reply and ideas. I appreciate it and they are a great help.
I'll have to open the amp again and see if I changed out the 220k's. It's been years. If not I'll try that. I'll also see what's installed cap wise. I believe stock that the Bandmaster TFL5005D had a 5uf. I may have went to 10uf but probably not 25uf.
K40Y-9 take 50 hours to sound good and 200 hours to fully break in.
220K on the power tube grids does not change the sonic signature. It keeps the power tubes from running away.
I'd had some 5mfd/50VDC caps a long, long time ago. Used 10mfd/50VDC and even 25mfd/50VDC. No difference in the tremolo tone, that I can tell.
An 8mfd/150VDC Sprague ATOM will fit, in that position. AES now stocks 5mfd/50VDC ATOMs.
I wonder if I have the wrong tube in the spot. I'll have to check on it.
I am not sure I would go with 6U8 or 12DW7 phase splitters. Any 12AU7 as in 1/2 of the 12DW7 are not good sounding tubes. I know a phase splitter is not as critical as preamp circuits, but every tube counts. 6U8s are ok, but still not an audio tube.
The best 12DW7 by a long shot were CBS 12DW7s. They are very rare now. It may take over a year just for one to show up on ebay.
I do not see your link for Fisher mods, but I will share exactly what I performed.First I built a new RIAA with discrete components plus the fix for better low end. Frankly, I heard no difference from the stock RIAA.
I replaced all coupling capacitors with K40Y-9 including the phono section. I lowered the 7868 or 7591 with 220K grid resistors and changed the .047uF to .068uF at the power tube grid.
The power supply doubler changed to 2x 680uF 400 volt capacitors. Added a poly type 10uF capacitor on the doubler output. Change rectifiers to UF4007. Kept screen at 40uF, all others at 50uF.
Added two 3500uF for the bias supply & changed bias bridge rectifier to UF4007;
Used short plate Westinghouse 12AX7 or Brimar CV4004 in phono section. These tubes greatly clean up the phono section. Preamp section used RCA 12AX7 tall plate. Either black or grey are good with no noise issues like some black plates. Used vintage Tung Sol 12AX7s at phase inverters. RCA or Sylvania 7858 or 7591 finishes the tubes. Should mention a 12AT7 was used in the multiplexer output regardless if marked 12AX7.
After these mods, the clarity was greatly improved. The phono section was stunning- such a difference. It had a little chime in the audio that made it so musical sounding. Chime being like a church bell ringing if that makes sense.
Edits: 11/29/16
Sony, thank you. I have to open mine again to see what I used for the doubler etc. I know that I increased it but I can't remember to how much. I forsure did not add the poly cap.
Here's a link to my post with the links to Dave Gilespie tweaks.
http://audioasylum.com/forums/vintage/messages/23/237783.html
Believe it or not I actually liked Cornell Dubilier DMT caps in the output stage more so than the russian PIO's. They are polyester film/foil. It could have been that I didn't give the k40's enough time to run in etc but I've liked them in other rebuilds. I had the DMT's installed first so I may also have grew use to their sound.
http://www.mouser.com/ds/2/88/DMT-12545.pdf
http://www.mouser.com/ds/2/88/DMT-12545.pdf
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