Here is my latest work on one of my .01 units. Used copper buss wire for lowest distortion.
Ok I am impressed. I own two 01s anda 215, all of which could stand new filter caps.——————————————————————————–
Its been twenty something years since I did some time on a repair bench, professionally at least. I was never a crackerjack electronic tech which is why I managed the repair center, cause that was where my true talent lies. Still I would do an 8 hr shift once a week, repairing stereo gear, and given enough time i generally could figure it out and the experience gave me enough knowledge to deal with customers, suppliers, and manufacturers. That was two careers ago. Left the field to be a Fleet Manager for a healthcare provider and when that ended I became an EMT, which is what I do now.
Enough of the history. I am downsizing my stereo to a receiver, CD player and cassette deck but keeping the the speaker system of satelites and sub woofer. I need to keep an amp to power the sub, and the choice appears to be a SWTP tiger 215 that I built in the early 70s. I also have some Tiger 01s but they are going along with the other equipment. The Tiger 01s have developed a power supply hum and though the 215 does not exhibit this problem I want to replace the filter caps on all of them thus making the 01s more saleable.The caps in both the 01s and the 215 are Mallory 4000 mfd 50 volt units measuring 35mm by 80mm. Searchig the web these are no longer available and the current 4000mfd units are about a third the size. I can get some Nichicon 10,000 mfd units with the correct connections and the same size at a reasonable price. Question is what problems am i looking at upping the capacitance by a factor of 2 1/2. i f I remember my Power Supply 101 course I need some kind of bleeder or bypass cap to keep the transformer from seeing a dead short while charging these behemoths. Looking at the SWTP cicuit board there is a small ceramic cap across the terminals on both caps. It is marked 1/10/250v. Will this be large enough with the new caps? The Transformer is +- 37volts TP 40mv. Thanks in advance for any help. Jim
I used some Mallory units. They are 4700 mfd and same dimensions as original. Newark has them. If you don’t mind matching the case you can get standard radial lead units or snap ins for a couple of bucks each vs the $20 or so each for the Mallorys. Btw they say Cornell Dublier rather than Mallory. Same company.
I should have responded that those .1 uF caps on the main power supply capacitors are just for bypassing them and lowering their impedance; they will also reduce (slightly) the inevitable RF switching noise of the rectifiers. A series RC consisting of about .1uF and 100 ohms across the transformer secondary on the rectifier board will act as a ‘snubber’ to more effectively reduce said noise, however slight its contribution. Keep the leads as short as possible and make the snubber cap a very low ESR type for best results.
Minor but I think worthwhile tweaks especially on the .01s.
I replaced the original caps in my 01s with 22,000 uF @50v Phillips computer grade caps. I also replaced the rectifiers with higher current HEXFRED types to handle the additional current surge, but found that 3 amp rectifiers were reliable enough.
Otherwise, a thermistor in series with the AC line could be used to limit the current surge.
Low-medium power 1kH distortion runs around .005%; higher power and current do display more high-order distortion components than I’d like to see, but the units seem quite stable. I think I got some further improvement in the latter distortion with MJ21193/4 output devices, which have better current linearity.
I wouldn’t recommend going as high in capacitance as Damon did, but his advice is sound. Though such a thermistor would have to be very carefully chosen such that it wouldn’t inhibit full audio power output. I would definitely up the ratings on the rectifiers if I was going to go double or more on capacitance. The stock rectifiers blew in mine long ago! The transformer and power switch will also be under additional strain. The small caps mentioned by James are no help against inrush current, they are there to make the big caps more “perfect” as large electrolytic capacitors have a bit of ESR and even a little ESI (Equivalent Series Resistance).
If the caps are good the amp will play for a while at a low volume after it is switched off. One test I’d suggest for testing the old caps would be to pull the + and – fuses, load each to ground with a large resistance, like maybe 10K, switch off and see how long it takes them to drain. What you really don’t want to see is one polarity run down much faster than the other. Of course any hum is an obvious sign too.
There is also a small electrolytic cap in the feedback loop that can affect bass response if it degrades.
Beware of most of the modifications suggested on the net or audiophile magazines. Many sacrifice slew rate and high frequency response in hopes of greater stability. Others are just plain daft! Two of the amps Kurt has were extensively modified and really didn’t sound very good. Turns out, they couldn’t even obtain a proper class AB2 bias.
The link above is a suggestion for safe testing of a power amp.
Thanks for the nice post Anton. The “Tree” would be a nice add-on for the Fester Tester!
The longish leads to the rear panel fuseholders and back to the driver board with little or no bypassing on the driver board seemed to invite possible stability problem; I tried a couple of axial lead 10uF caps connected directly to the rectifier board’s central ground. No changes were observed or measured on a Tektronix AA501A distortion analyzer, so this is probably just gilding the lily. I removed them for the time being.
I’ve now replaced all the electrolytics, including the feedback 220uF capacitor, and will replace all of the carbon film resistors with metal film resistors with far lower noise and temperature coefficient, but audible changes/improvement will probably be marginal.
Currently using my .01s while I repair/overhaul my Leach amplifiers. The .01s aren’t _quite_ as ‘open’ and detailed, but they do sound good compared to a few very high end and extremely expensive amplifiers I’ve had opportunity to listen to in recent years. And completely stable, as far as I can determine.
The wiring to the fuses and such is usually not a problem as long as they are all kept inside the metal bracket that holds the heatsink and PC board, and kept low by the floor. I saw one once where the guy attached the wires to the topside of the PC and had a mess of wires running over the topside of the PC and that wasn’t good, picked up stray RF easily when the covers were off. But bypass caps wouldn’t hurt anything, I’d us 0.1s with 100V or better rating, use ground on the PCB and keep the leads short.
The 5% resistors may be metal film already, you have to remember the age of the parts, MFs were commonly available in 5% back then. Now they are mostly one or two percent and may carry an extra sig. digit band, which makes the multiplier band one less. All MF and CF resistors are inductive to a some degree, but some are less so, a they reverse the spiral cut half way through (or more).
Never heard of the Leach amps, tell me more.
The .01, properly built, is a stable amp. Things to watch are excess RF in their environment and issues with floating grounds or ground loops. I generally made the jumpers from amp to preamp myself. Some amps have the input connector isolated from the panel and then tied to ground via a small resistor to avoid ground loop oscillations. Haven’t tested this on a Tiger but I wonder if it wouldn’t be a good idea.
I’m still looking for a toggle switch to match the original, full sized, flat, tapered lever. I can easily find smaller sized switches of that style, but not full size. If anyone sees them, let me know!
Ditto on the toggle, I have one shorn off I would like to replace!
On the transformer versus the cap size…the transformer DC resistance will self limit on charging any sized cap. A surge limiter should work fine also as I have put these on some Pioneer amps that had the weak diodes.
The stability problems showing up as thermal issues are due to the Szklai output stages which are prone to HF oscillation and should be neutralized as best possible.
Your email address will not be published. Required fields are marked *