Holy Or Hell: Ace & Steve Update 2 – The Heartbreak Of Vintage Gear
Ace and Steve’s Big Vintage Summer Adventure
Update No. 2:
The Heartbreak of Vintage Gear
by Steve Graham
This was originally going to be a much different progress report. I’ll get into that later, but let’s start with the really bad news, progress to the discouraging, then end with the cautiously hopeful.
The sad case of two Fishers. (Fisher 20A Monoblocks) Ace had given me carte blanche, with the only condition being I not purloin the output transformers. The plan was to perform a major parts replacement, consisting of most resistors and all capacitors, but leave the transformers, input jacks and speaker connectors in place. But I got part way into stripping the Fishers and found that the output transformers in both monoblocks were bad, honest. I have the measurements and pictures of the measurements to prove it. Both output transformers failed on the same section of the primary winding. I’m waiting for Ace’s direction as to whether we just abandon them, set them aside in hopes that an opportunity to press forward will present itself, or wait for some divine intervention. My trusty editor finds the Fishers so repulsive-looking, that he’d be happy to see them melted down to become rebar or truck bumpers (Editor’s note: I never said that! But I do believe Fisher gear is the reason stereos were relegated to basements). Not exactly the supportive boss one needs when the chips are down. A snazzy paint job, some gold-plated jacks and connectors and a sweet-sounding circuit just might make them desirable, almost.
At this point I have to come clean. I had assumed – yes, I know, assumption is the mother of all screwups – that the Fishers’ transformers were good, so I went ahead and bought replacement capacitors and resistors. For better or worse, I’m invested in this project. I’m also a sucker for waifs, strays and hard luck cases. Sure, the Fishers are butt-ugly, but to me that’s part of their charm. I hope that a solution can be found and someday they’ll become the ugly ducklings that morph into beautiful-sounding swans.
Someone suggested that I have the output transformers rewound. My guess is that this would likely cost at least 500 dollars. Too much to sink into old amplifiers of questionable performance. Even a new pair of generic Hammonds start at around 300 dollars, all in. I’m pretty sure I could make a decent-sounding pair of amps around what’s left of these, but that’s Ace’s call and I understand his reluctance to make it.
I know all of you purists are about to burst a blood vessel. You are freaking out that I’m destroying a piece of audio heritage. Take a pill, as we used to say in the seventies. Fisher already spoiled the party with their substandard components. And don’t get me started on how Fisher was running the output tubes way over their maximum recommended voltage and at 100% of their power dissipation when sixty to seventy is more typical.
The Leak Stereo 20, so close but not quite there. As reported last time, the Leak was progressing nicely. But another assumption has come back to bite me. I finished a minimum burn-in cycle with the Leak playing streamed music into a dummy load for about seventy hours. The Leak on its own is quite quiet, but as it was playing into the dummy load, I hadn’t noticed one critical thing: the Leak doesn’t play nice with other components. To varying degrees, any component plugged into the Leak results in hum on the output that could be heard when connected to speakers. The least amount of hum was with my PS Audio DirectStream DAC plugged directly into the Leak. The PS has a digital volume control so its output is controllable. The hum was still audible but only with my ear pressed against the speaker. The PS uses transformers to couple its output to the outside world and it’s that I think was responsible for the lowest amount of hum of all the components I had available. But any other component plugged into the Leak, even ones that play nice with other amps, yielded too much hum.
The Stereo 20 was so close to perfection. (Sigh) It was sounding really promising when fed by my PS DAC. Noise issues, hum included, can be some of the nastiest to track down in a stereo component. Unfortunately, there isn’t a piece of test equipment, at least not one that I own, that will point the finger at the problem. It’s just work and dumb luck that will find and fix this gremlin. One big obstacle to troubleshooting is the construction method Leak used. I’m sure they only expected their amps to be used for ten of fifteen years, then be scrapped or traded. If the sticker on the underside of the Leak chassis is to be believed, it was built in 1960. (See one of the pictures below.) I’m sure back then no one at Leak, or any other equipment manufacturer, expected their gear still be in service sixty-two years later.
The wiring board, sometimes called a ladder board, where most of the passive components are mounted, is easily accessible. The wiring harness that connects everything together occupies the ~1/2” space between the board and the inside top of the chassis. Unfortunately, the board is held in place with three automotive style, push-on clips (picture above). Removing these would, I’m sure, destroy them.
As well, the wiring harness bundles all wiring, filament, B+, signal and grounds together (pictures above and below). Even in 1960, amplifier builders were realizing the value of twisting filament wiring (picture below shows how NOT to do it) and routing them far as possible from signal-carrying leads. In fact, any wiring carrying or susceptible to AC signals should be twisted pairs. Leak, I’m sure, knew of these practices but chose to ignore them to minimize assembly times.
I’m just too stubborn to give up on the Leak. As well, I’d like to hear for myself if David Neice’s affection for the Stereo 20 is justified. I’ll try a few more things, but if I have to get radical, I will. Vintage lovers fear not. I won’t change the circuit, but layout and wire routing might need “adjustment”.
The Mactone X-21. I haven’t quite come to terms with the Mac, but I think there’s a way forward. Though not strictly necessary, I’m going to bring the AC line wiring up to current electrical code. I’ve installed the proper tubes – I suspect that at some point sub-optimal ones were used – but now it’s adorned with NOS beauties from GE and Mullard. A little bit of tidying up and I’ll be ready to put it to the test.
I have a new-found respect for techs that work on vintage gear. If talent and a good dose of luck is on their side it will be smiles all ‘round. But the odds are stacked against them as far as I can see. Hero to zero is a tightrope they walk every day.
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Have you confirmed that Hammond makes an output transformer with the same specs as the Fisher original? If they do and it’s $300 for a pair, consider that to be a good deal. I just paid $150 for a single power transformer for a Quad classic 2 amp. Output transformer design and build is more complicated and if I needed one and could get it for $150, I’d jump at the chance, before the price inflates.
Thanks for the encouragement. The latest news on the Fishers is that they will likely live to sing again. We are taking a bit of a leap of faith and selecting the same or very similar transformer to the one used in my EL84 build series. Maybe not the ultimate in performance but certainly good and a whole lot better than the broken Fisher “iron”.
Regards, Steve Graham
If the output transformer of a vintage amp is bad, most of its value is gone because this is by far the most expensive part. If you do buy new trannies, I would use ultralinear types and connect the screen grids of the 6BQ5’s to the taps. Pentode connected 6BQ5’s to me sound harsh. Also, I would delete the common 125 ohm cathode bias resistor and 50uF bypass capacitor, and use a separate 330 ohm, 3W resistor and 47uF capacitor on each tube. This would bias each tube to a lower idle current, and allow each tube to set its own bias. Lastly, the split-load driver, to me, sounds awful. The long tail pair circuit, like that used in the Leak stereo unit, sounds much better.
Thank you for your input. I agree that a long tailed pair would be the preferred option and virtually a necessity with EL34s or more powerful tubes. EL84s are quite easy to drive so the split load works OK or OK-enough for a decent-sounding amp IMHO. Also, the chassis is cramped as it is. There is barely enough room for the four tubes now without adding another. I don’t want to give the game away too much before the amps are finished but grid stopper resistors will be incorporated as the original design didn’t have them. That will mean a bit more real estate required around the existing tube configuration. Point taken about ultralinear vs. pentode wiring but I’ll leave that up to Ace since he’s paying the bills.
Thank you for interest in Wall of Sound.ca
The Fisher 20a is very similar to the 30a, SA100 and SA16 and similar to the amplifier circuit in the X-100, early X-101 integrated amplifiers, 500s and TA-600 receivers. Output transformers for all are ready available and at a cost that is lower than $150 each. Fisher tended to use the same or very similar transformers across multiple models having related circuit designs. And a Fisher transformer would be an authentic replacement. I look forward to what you do because I have a pr of 20a and 30am amps that are completely stock (and 60+ yrs old).
Thank you for your interest. I’m sure your Leaks are in need of new electrolytic capacitors at the very least and maybe some coupling caps and resistors too.
Regards, Steve Graham