rayma has suggested that we start this thread with some guidelines to choosing a good (or bad!) candidate. Usually the choice is made when something falls into your lap, but if given a choice, what brands and even models are most promising? I'll start by saying that the only thing I'd recommend for a beginner to avoid is an amplifier with 7591/7868/other last generation output valves. These were made in a time when manufacturing was at its peak and the horsepower races were too. Output valves were run hard and put up wet, and current manufacturing is unable to make really solid replacements. Other folk may differ, of course.
Hopefully, if this thread progresses well, we can include topics of safety, troubleshooting both general and specific to these old parties, test equipment including DIY and modern DAC/ADC plus software methods, and best practice dealing with aged capacitors, etc.
So, safety first last and always. There's a very lengthy sticky thread on safety that covers a lot of ground, but I'll add mine here. Keep one hand in your pocket. Better yet, attach test leads with power off, then keep both hands in your pockets. Current hand-to-hand goes through your heart, and you're a dead peckerwood. Make something to bleed down voltage AND have a dedicated DC voltmeter connected across B+ at all times. Cost about $15 - $20 and a cheap layer of protection. Keep kids, pets and impulsive friends on the other side of the door. For soldering, wear eye-pro. Make a strong habit of looking AGAIN at the unplugged end of the power cord every time you approach the patient.
Maybe enough to begin, Next!
All good fortune,
Chris
Hopefully, if this thread progresses well, we can include topics of safety, troubleshooting both general and specific to these old parties, test equipment including DIY and modern DAC/ADC plus software methods, and best practice dealing with aged capacitors, etc.
So, safety first last and always. There's a very lengthy sticky thread on safety that covers a lot of ground, but I'll add mine here. Keep one hand in your pocket. Better yet, attach test leads with power off, then keep both hands in your pockets. Current hand-to-hand goes through your heart, and you're a dead peckerwood. Make something to bleed down voltage AND have a dedicated DC voltmeter connected across B+ at all times. Cost about $15 - $20 and a cheap layer of protection. Keep kids, pets and impulsive friends on the other side of the door. For soldering, wear eye-pro. Make a strong habit of looking AGAIN at the unplugged end of the power cord every time you approach the patient.
Maybe enough to begin, Next!
All good fortune,
Chris
Hi Chris,
There is this debacle of mine, discussed here ... Pioneer SM-R150
It sits next to me on the desk where I work, upside down with its entrails hanging out, reminding me that I lack the experience to make the right decisions about its fate.
Output tubes are 6AR5, a miniature 6F6, so need some extra swing to drive them over 'normal' candidates.
I recapped it, but although the sound was improved, it also showed up a lot of the limitations of the design. I had tried to retain the top level appearance, and only replace suspect or critical components underneath, so it has not strayed too far away from its original design.
I do not need the old crystal cartridge and tape head inputs, so I have removed the input selector which had all the equalisation components for the other sources bonded to it along with a couple of tag strips. I will replace it with just a MM input, and 2 normal line level inputs.
Now I am stuck, though. Do I try to faithfully rebuild it, or do I try to use some 'best practice' solutions and create something different? I have simulated the following:
I was ready to go down this path, and then I decided to simulate the whole amplifier from line in, and it looked to me like I would lose too much gain through the tone stack I was planning, so I would not have sufficient drive for the output stage. Then I started to think that maybe 6AQ5s as the output tubes could be an option?
Then I looked at the Phone stage again. I simulated some different solutions and started a thread about it here: 12AX7 Phono stage shootout on LTSpice. At that point I was thinking rebuild it as a Harmon Kardon HK300, but I was struggling to get the simulation to look OK, and it is nice to build something that is also simulated, as an aid for testing. From that shoot out the existing Phone stage did not look too bad. It is active, which I quite like, and it was just the input impedance (30k) that was obviously not right.
So I am in a hole, and this thread is a welcome place to seek guidance.
Cheers, Richard
There is this debacle of mine, discussed here ... Pioneer SM-R150
It sits next to me on the desk where I work, upside down with its entrails hanging out, reminding me that I lack the experience to make the right decisions about its fate.
Output tubes are 6AR5, a miniature 6F6, so need some extra swing to drive them over 'normal' candidates.
I recapped it, but although the sound was improved, it also showed up a lot of the limitations of the design. I had tried to retain the top level appearance, and only replace suspect or critical components underneath, so it has not strayed too far away from its original design.
I do not need the old crystal cartridge and tape head inputs, so I have removed the input selector which had all the equalisation components for the other sources bonded to it along with a couple of tag strips. I will replace it with just a MM input, and 2 normal line level inputs.
Now I am stuck, though. Do I try to faithfully rebuild it, or do I try to use some 'best practice' solutions and create something different? I have simulated the following:
- RCA RIAA input stage, line level out. Uses the existing ECC83s (1 per channel).
- Volume control on all line level inputs, and then a Baxendall type tone stack. Also uses the ECC8ss (1 per channel)
- Balance control. (A big feature of this amp is this 'mechanical tuning scale' type display for the balance levels).
- Keep the existing output stage - driver plus phase splitter (1 ECC83 per channel) and 6AR5 outputs.
I was ready to go down this path, and then I decided to simulate the whole amplifier from line in, and it looked to me like I would lose too much gain through the tone stack I was planning, so I would not have sufficient drive for the output stage. Then I started to think that maybe 6AQ5s as the output tubes could be an option?
Then I looked at the Phone stage again. I simulated some different solutions and started a thread about it here: 12AX7 Phono stage shootout on LTSpice. At that point I was thinking rebuild it as a Harmon Kardon HK300, but I was struggling to get the simulation to look OK, and it is nice to build something that is also simulated, as an aid for testing. From that shoot out the existing Phone stage did not look too bad. It is active, which I quite like, and it was just the input impedance (30k) that was obviously not right.
So I am in a hole, and this thread is a welcome place to seek guidance.
Cheers, Richard
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This would include the Ami Rowe amplifiers from Juke Boxes, and there is a thread here: Ami Rowe R4359A. My first tube amp was one of these that had been converted to 6L6 outputs, and it looked like quite a trivial change. The sockets fit OK, and the OPT has a plethora of output impedance options depending of how it is wired.
I also have a cunning plan for one of these. There is a 100VCT secondary for use as an output for 100V remote speaker systems. It looks to me that something vaguely similar to an EAR509 could be possible, with EL509 as the output tube, and the screen driven from the 100VCT secondary. Might even be able to sacrifice and use the existing sockets, getting them to accommodate the wider pins of the magnoval tube.
In general it is a lot more difficult to restore an old integrated amplifier then a plain amplifier. To deal with the under-chassis rats nest of some vintage amplifiers is taking things to another level.
Hi Richard,
If I can find anything useful to comment, I'll answer on the threads you've already started, to not violate the board's rules against multiple threads on the same topic. I'd hoped that this thread could become a general knowledge thing to which we could refer newcomers just getting their feet wet. But it doesn't look like anybody's interested. C'est la vie.
All good fortune,
Chris
If I can find anything useful to comment, I'll answer on the threads you've already started, to not violate the board's rules against multiple threads on the same topic. I'd hoped that this thread could become a general knowledge thing to which we could refer newcomers just getting their feet wet. But it doesn't look like anybody's interested. C'est la vie.
All good fortune,
Chris
Out of interest, what is the proper scope of 'Golden Age amplifiers'?
There are those out there who think it all went to hell when they kicked the globes out and heated cathodes indirectly. There are also those that dismiss the console amplifiers, but revere the famous names (Leak, Quad, HK, McIntosh, Radford, etc) of the 50's and 60's.
Is it a broad church?
Other sites like Vintage Radio UK also cover this topic. Because they have covered these consumer amps in the past, google sends people back to them, so it is self perpetuating. The threads stray from topics favoured on DIYAudio since they often cover items like crystal catridges, scratchy potentiomers, threading the tuning dial, and the more contentious discussions about stuff caps/reform/replace and 3 wire mains supplies. I am not so sure there is much stomach for those debates here, so maybe it will end up as horses for courses and old amps will not not get the coverage on this forum.
There are those out there who think it all went to hell when they kicked the globes out and heated cathodes indirectly. There are also those that dismiss the console amplifiers, but revere the famous names (Leak, Quad, HK, McIntosh, Radford, etc) of the 50's and 60's.
Is it a broad church?
Other sites like Vintage Radio UK also cover this topic. Because they have covered these consumer amps in the past, google sends people back to them, so it is self perpetuating. The threads stray from topics favoured on DIYAudio since they often cover items like crystal catridges, scratchy potentiomers, threading the tuning dial, and the more contentious discussions about stuff caps/reform/replace and 3 wire mains supplies. I am not so sure there is much stomach for those debates here, so maybe it will end up as horses for courses and old amps will not not get the coverage on this forum.
I had taken it to mean the post-War "HiFi" era, especially the time of the convergence of microgroove records, tape recording, FM radio, and a post-War boom market able to support lots of startup firms with fresh ideas. Roughly the era (in America) of RCA shaded dogs and Mercury Living Presence, and the era of the great expat European conductors of American orchestras who got recorded on them. About 1963, all that ended, although the production of great vacuum valve amplifiers continued and expanded for quite a while.
Consoles and old radios and such are really only for the most dedicated. It's difficult to discuss them publicly because they're such a fire and electrical safety liability, and don't sound that wonderful anyway. Not for the faint of heart, and probably not generally suitable for diyAudio Tubes/Valves.
That would be my take on it, all good fortune,
Chris
Consoles and old radios and such are really only for the most dedicated. It's difficult to discuss them publicly because they're such a fire and electrical safety liability, and don't sound that wonderful anyway. Not for the faint of heart, and probably not generally suitable for diyAudio Tubes/Valves.
That would be my take on it, all good fortune,
Chris
Only experience with tube fryers
was MI amplifiers.
Numerous Music man and Traynors
were dirt cheap used in the 90's / 2000 era
music stores. Running very high watt war
plate voltage. Nobody wanted them.
Fried tubes.
We loved them. 7591 / EL34 / 6CA7 amps.
got Chinese 6L6 and 6CA7.
Recapped power/bias
Doubled screen resistor values.
gave up on the myths
the chinese tube lasted.
LOL oh well
Everyone peeved and whined about
UL / Ultra Linear amps.
My tube fryer Fender 135 with UL
did the best with 6L6 chinese as
well. Everyone said use 7591
Nope
was MI amplifiers.
Numerous Music man and Traynors
were dirt cheap used in the 90's / 2000 era
music stores. Running very high watt war
plate voltage. Nobody wanted them.
Fried tubes.
We loved them. 7591 / EL34 / 6CA7 amps.
got Chinese 6L6 and 6CA7.
Recapped power/bias
Doubled screen resistor values.
gave up on the myths
the chinese tube lasted.
LOL oh well
Everyone peeved and whined about
UL / Ultra Linear amps.
My tube fryer Fender 135 with UL
did the best with 6L6 chinese as
well. Everyone said use 7591
Nope
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I've recently restored an RCA RS177H console pull amp. The build is detailed here:
https://audiokarma.org/forums/index.php?threads/rca-console-pull-project.977520/
It was pretty ratty to start, but ended up as a nice-sounding, pretty little amp to power my shop speakers.
https://audiokarma.org/forums/index.php?threads/rca-console-pull-project.977520/
It was pretty ratty to start, but ended up as a nice-sounding, pretty little amp to power my shop speakers.
Attachments
My 2ct.:
High level overview:
Audio Research Corporation D90: much underrated, therefore affordable
McIntosh MC240: much overrated, but if you can find one for a good price, worth looking into.
High level overview:
- Avoid integrated amps: they’re usually built to a price point and are more trouble than they’re worth.
- For power amps, avoid those with a single low-level tube: they’re also built to a price point. Unless you’re sure they have good output transformers (OPT) and plenty of room for some heavy duty moddings, like the Dynaco.
- The OPT’s are the most critical components in a tube amp. Sadly, nearly every manufacturer hides their worth, or lack thereof, behind tons of marketing BS. The very best ones, like the Hashimoto/Sansui or the ISO/Tango are still being made; they only cost you around a kilo buck a pair! I remember drooling over a pair of Sansui OPT with their individual frequency response curves; I was only a pre-teen young boy then.
- The high voltage power supply should be made as stiff as possible. Forget all engineering good practices, use a ruler, and figure out how much capacitance you can fit safely inside the chassis. Yeah, by volume!
- All components should be replaced.
Audio Research Corporation D90: much underrated, therefore affordable
- Pro:
- Very good OPT
- Classic Mullard-like circuitry, unlike other ARC amps
- Con:
- Poor thermal design: all electrolytics are cooked way pass well done.
- There’s an idiotic active phase inverter at the input, feeding one half of a totally balanced push-pull circuitry. ARC used to do this to all their amps.
- Fix:
- Add a low speed fan
- Pro: good OPT, classic Mullard circuitry
- Con: may not come cheap.
- Pro: good OPT
- Con: cheap original design
- Fix:
- Fit one of the many upgrade PCBs: the better ones turn the Dynaco into a Mullard circuit.
- Pro: good OPT
- Con:
- Poor design starving the low-level tubes.
- Too much feedback.
- Fix:
- Run low level stages at higher current.
- Reduce feedback.
McIntosh MC240: much overrated, but if you can find one for a good price, worth looking into.
- Pro: great OPT. Roger Modjeski (RIP) once said, jokingly: it took a lady a whole day just to terminate one single OPT!
- Con: very unpleasant sounding due to the class B operation
- Fix:
- Bias way into class AB: I run mine at 55mA
- Minor circuitry change (maybe I’ll publish what I did one day)
- Pro: very good OPT
- Con: very soft sounding amp.
- Fix: difficult, I tried and failed: the closest I got was with SS rectification, and 6L6GC tubes, but still it wasn’t totally satisfactory. Maybe it needs a complete rethink à la Turner (RIP). Best of luck!
That is a good selection of the 'top tier' amps.
There used to be a site '100 amplifiers to lift your hat to', from Lilienthal Engineering that covered the bulk of the cream of the cream.
I found this reference to it ... 100 great amplifiers part 4, 59-82
There used to be a site '100 amplifiers to lift your hat to', from Lilienthal Engineering that covered the bulk of the cream of the cream.
I found this reference to it ... 100 great amplifiers part 4, 59-82
The original RS177 amp in my RCA Victor console is pretty decent even by today's standards.
However, I decided to not just restore it, but redesign it.
Upgraded to a bit better output transformers, (Concertone) used 7189A output tubes, and 12AY7's as drivers/phase inverters.
It's still using the original 1963-vintage 5AS4A rectifier!
Redesigned the power supply, and beefed up the reserve capacity to the RCA am/fm tuner/preamp chassis.
It kicks butt now.
Great posts. I've found from my limited direct exposure to older tube amps here in the midwest that golden-era kits
can be good candidates, but the assembly work by a hobbyist can be poor, and if the unit is hard-wired (no pcbs),
this can be a lot of work. If you plan to rip everything out and replace with all new parts, this is not such a problem,
but beware of OT leads that were cut too short. This goes for the power transformer as well.
Also beware of cloth transformer leads that are brittle and cracking from long term heat exposure.
If for your own use, there is no good reason to retain obsolete features like ceramic cartridge or tape head inputs.
And this is a good time replace the cheap RCAs, speaker terminals, and volume control with better parts.
It is possible to salvage boards in good condition, but replacing them with new boards is better and less work,
allows the circuit topology to be upgraded, and better parts can be used that would not fit the old boards.
can be good candidates, but the assembly work by a hobbyist can be poor, and if the unit is hard-wired (no pcbs),
this can be a lot of work. If you plan to rip everything out and replace with all new parts, this is not such a problem,
but beware of OT leads that were cut too short. This goes for the power transformer as well.
Also beware of cloth transformer leads that are brittle and cracking from long term heat exposure.
If for your own use, there is no good reason to retain obsolete features like ceramic cartridge or tape head inputs.
And this is a good time replace the cheap RCAs, speaker terminals, and volume control with better parts.
It is possible to salvage boards in good condition, but replacing them with new boards is better and less work,
allows the circuit topology to be upgraded, and better parts can be used that would not fit the old boards.
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Heathkit amps could be good candidates. Some have good OPTs like the Acrosound (Dynaco); it's just hard to tell which ones have them.
Most of the better ones are based on the Williamson circuit, which can be temperamental. Dealing with the ratnest is pretty much unavoidable, since most of the carbon resistors must have drifted way out of spec. Just call it an extra incentive to change to a more simple circuit like the Mullard.
Also worthy of mention are the Eico HF60, the Fisher SA-100/200/300, and so on.
Most of the better ones are based on the Williamson circuit, which can be temperamental. Dealing with the ratnest is pretty much unavoidable, since most of the carbon resistors must have drifted way out of spec. Just call it an extra incentive to change to a more simple circuit like the Mullard.
Also worthy of mention are the Eico HF60, the Fisher SA-100/200/300, and so on.
Also the golden era kits have good manuals which can usually be easily found on the web. Just a few sources:
https://www.vintage-radio.info/heathkit
http://www.tubes4hifi.com/downloads.htm
https://bama.edebris.com/manuals/
https://www.schematicsunlimited.com/
https://www.vintage-radio.info/heathkit
http://www.tubes4hifi.com/downloads.htm
https://bama.edebris.com/manuals/
https://www.schematicsunlimited.com/
Heatshrink tubing can be slipped over old wiring to insure reliability.
Mine would be, too except for the fact that I dropped it and shattered the glass. It tested fine.
It wasn't too hard to find a NOS replacement, however.
A 5U4GT would work too.... I've got a stock of GE, RCA replacements hidden away.
The 6FQ7's replaced with the 12AY7's also took some load off the power trans too, which tends to run hot.
The 6FQ7's replaced with the 12AY7's also took some load off the power trans too, which tends to run hot.
"I'll start by saying that the only thing I'd recommend for a beginner to avoid is an amplifier with 7591/7868/other last generation output valves."
Respectfully disagree, Chris-
Our house heavily uses my Pioneer SA-810 PP output bank cloned to Dynaco ST-35 pre / phase splitter....
For 2 years... Ask the neighbors 😊
Altho havent measured plate currents, fixed bias set -19V into PP 6GM5's w/ no failures- so far...
"Output valves were run hard and put up wet"
"current manufacturing is unable to make really solid replacements"
First part- Dayum son
Second- JJ and ChiFi have Repro 7591's
https://www.tubesandmore.com/products/vacuum-tube-7591-jj-electronics
Respectfully disagree, Chris-
Our house heavily uses my Pioneer SA-810 PP output bank cloned to Dynaco ST-35 pre / phase splitter....
For 2 years... Ask the neighbors 😊
Altho havent measured plate currents, fixed bias set -19V into PP 6GM5's w/ no failures- so far...
"Output valves were run hard and put up wet"
"current manufacturing is unable to make really solid replacements"
First part- Dayum son
Second- JJ and ChiFi have Repro 7591's
https://www.tubesandmore.com/products/vacuum-tube-7591-jj-electronics
