Rex Runner
Tobes of Hades lit by flickering torchlight
I did need the Sams
That's awesome
Much appreciated
That's awesome
Much appreciated
OUTPUT TRANSFORMERS
- Thread starter Rex Runner
- Start date
I have a console amp that had a torched power transformer. It was in a similar state cosmetically too. Cap underneath shorted and exploded, and the transformer roasted. No fuses or breakers, no idea what finally cut the power but the transformer was not open circuit. It was shorted though. It cleaned up fine with mineral spirits on a rag.
The chassis is the only thing I really ended up using on that build. Power trafo came from Knockbill off an unknown device, the outputs were "good" but useless so it now has Hammond tone cabinet iron, and of course all of the cap were bad. It retains basically the original circuit, most of the resistors, and the sockets.
oh, and I did add a fuse to it. I suggest you do the same.
The chassis is the only thing I really ended up using on that build. Power trafo came from Knockbill off an unknown device, the outputs were "good" but useless so it now has Hammond tone cabinet iron, and of course all of the cap were bad. It retains basically the original circuit, most of the resistors, and the sockets.
oh, and I did add a fuse to it. I suggest you do the same.
Rex Runner
Tobes of Hades lit by flickering torchlight
Much better
Rex Runner
Tobes of Hades lit by flickering torchlight
Looks like ill have to paint her up
Any color suggestions?
Any color suggestions?
Nice work on the cleanup!
If those are phenolic formaldehyde sockets (resin and paper) you might want to replace them with something better.
An autobody shop can bake on an enamel for you that will look really spiffy. If you mask it the sockets and capacitor can the price will be very reasonable.
You can always try some fine metal polish to remove any of the residual oxides and leave it mirror bright, which is another option. Not sure if the plating was damaged or just oxidized.
If those are phenolic formaldehyde sockets (resin and paper) you might want to replace them with something better.
An autobody shop can bake on an enamel for you that will look really spiffy. If you mask it the sockets and capacitor can the price will be very reasonable.
You can always try some fine metal polish to remove any of the residual oxides and leave it mirror bright, which is another option. Not sure if the plating was damaged or just oxidized.
not a fan of wafer sockets either. They weren't amazing when new and they don't improve with age and use.
I've actually never painted any of mine. Mostly because I'm lazy and to get a good finish it needs the transformers and such stripped. You're already there though.
I've actually never painted any of mine. Mostly because I'm lazy and to get a good finish it needs the transformers and such stripped. You're already there though.
Rex Runner
Tobes of Hades lit by flickering torchlight
Question for the pro,s.....Need a power transformer. Sam,s reads it's a 620vct with 310v going to rectifier. Can I go higher or lower on voltage or MUST it be the same? Any input always appreciated. Rex in Ohio
10v up or down from that figure should work if you cant find an exact match.
It depends.
The issue is that all of the voltages are typically based upon both the mains voltage, lower in those days, and a specific output voltage. If the output voltage is higher or lower than such things happen as (a) the load line will slightly shift, generally not significant, and (b) the tubes, if run higher, will suffer the deleterious effects of the concomitant higher power dissipation and thus have a shorter lifespan, which can be significant.
Some of the older amplifiers pushed the output stage to the tube's limits. I have one which obtained 20 WPC from a push-pull 6BM8, which is not a good idea. The voltages used are the limits of the datasheet, which is why the chassis is scorched under one side when one output tube melted down and took the output transformer with it to Valhalla.
Adding dropping resistors is a poor regulatory technique because the load varies with drawn current. A better one is using a zener diode as a regulator. Yes, the zener is noisy, and this worsens with breakdown voltage, but that noise can be dealt with by building a stack from smaller, less noisy devices, or filtering. Another is using a choke which has enough DCR to drop the voltage. It also stabilizes the supply. The best is finding the correct transformer as a salvaged part, which can often be done.
For real? Did you measure this? That's kind of impressive to be honest, although one step away from meltdown!
I agree with others about the voltage of the transformer. It shouldn't be hard to come up with something very similar, in any case.
Sometimes those old power claims are just out to lunch too, so take any claims from the mfg with some salt.
Its an EL84 push-pull amp, have a gander at something like a Magnavox 9300, a Pilot 232, or even a Dyna ST-35 for some idea of typical voltages. Anything that runs an amp at about 300-330vdc on the plates and has a total power output at roughly 25 watts should yield up suitable iron.
The Motorola doesn't sound unreasonable though. Also consider that likely had an outboard tuner or preamp that isn't there anymore, so the transformer is probably a little bit over-rated for the job. This isn't a bad thing, but it does give a little wiggle room on the specs if needed.
Its an EL84 push-pull amp, have a gander at something like a Magnavox 9300, a Pilot 232, or even a Dyna ST-35 for some idea of typical voltages. Anything that runs an amp at about 300-330vdc on the plates and has a total power output at roughly 25 watts should yield up suitable iron.
The Motorola doesn't sound unreasonable though. Also consider that likely had an outboard tuner or preamp that isn't there anymore, so the transformer is probably a little bit over-rated for the job. This isn't a bad thing, but it does give a little wiggle room on the specs if needed.
This amplifier is what made me believe it's possible http://www.ramlabs-musicreference.com/rm10mk2.html
Low idle current, low screen voltage, and very high plate voltage manage to get 35W RMS out of a pair of Russian 6BQ5's, which goes against everything I thought I knew... 20W out of 6BM8 seems reasonable too if same strategy is followed, but would be interesting to see it in reality.
For OP, a Hammond transformer with the correct specs would probably be the easiest path to getting going.
Worked the numbers from the schematic and manual and found it was running at the tube's peak, not steady state, limits. At least what was published in the data sheet.
The only way to meet those specs is to use the hardened Russian tubes and even there it's pushing it.
The amplifier had Chernobyled. One channel had the tube melt —removed by the previous owner and discarded, which was a shame as I would have saved it as a bad example—and the output transformer winding was burnt and the paper carbonized. My supposition was the tube failed by arcing and the resulting dump of B+ into the transformer melted it.
This is why old radios often used a capacitor between the plate and the output transformer. In case the tube failed the transformer wouldn't be destroyed.
I will rejigger the output to be within sane limits. Going to use it with headphones, anyway, so the extra power isn't needed.
We live in an ocean of stripped gear. Thirty years from now the supply of used transformers will no doubt be very different.
Rex Runner
Tobes of Hades lit by flickering torchlight
Correct on the Hammond. Saw some surfing the Bay.
Yeah, those numbers are usually delusional. But I was relying on the voltage in the manual which was at the limit in the datasheet. The Russian tubes are better, but I see no reason to run it that hot particularly when the output transformers obviously were too small to deliver that kind of power for very long.
Those fictitious output numbers led to the whole watts debacle where the FTC created a testing standard to address the routine lies by manufactuers. You likely remember Hafler's open letter about the change which forced Dyanco to reduce its claimed power output numbers. I'm not saying the FTC procedure was any good, just that's why it was created.
Or just get from an electronics vendor, there's many places you can buy a brand new Hammond without eBay risk
No surprise there! The 6BM8 can make what, 8W in a sane push-pull application? Those were very popular in European equipment, and the lowest end tube Japanese receivers.
The 6P15P-EV is the ruggedized version, able to tolerate higher voltage and higher plate dissipation than the European or US equivalents. So Modjeski's comment on the Dynaco's power output isn't exactly apples-to-apples, as those tubes were not widely available in the US at that time. I suspect that a conventional 6BQ5 would rapidly turn into slag in that amplifier.
I take a belt and suspenders approach, and will happily trade tube longevity, and a lack of visits from the fire department, against increased power output.
Mos def.
You can paint it any color you want as long as it is black.
(okay, I like black).
Yes, 8 watt is pretty much the design limit. Some manufacturers specify 7.
I believe a 20 watt amplifier from those days was what we'd today consider to be about 12 Watts. Lies, damn lies, and power ratings for amplifiers.
Which is where mine originated. I have a few Japanese amplifiers and receivers (Trio) awaiting rebuilds. The iron isn't great, so the low-end response suffers, but the build quality is typically very nice. OEM'd for all of the HiFi catalog companies.
In the 1950s and 1960s many of the Japanese manufacturers treated the power output limits as optional starting point. I'm reminded of an interview with Hafler where he recalled a discussion with Japanese engineers about the number of transistors Dynaco used (five, IIRC) vs. the number the Japanese engineers were permitted (three, IIRC). I thought it was Kittleson, but looked there and didn't see it. Anyway, the Japanese tended to push the device ratings to the limits, whether it was tubes or transistors.
One other suggestion. If you're going to paint it best to etch the surface for better adhesion. A first-rate primer is key. I've had very good results with the Benjamin Moore and Valspar universal primers. Even sticks to galvanized!
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