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"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz -
I just had a moment of clarity... For a primary impedance typical for el34 tubes you could use a pair of el37 tubes. I think they'll take the voltage and reduce the current requirements. I've never heard them, but I've read they sound very good. The amp would probably put out around 25W. Which is eminently more useful than the usual 50's and 100's in most cases.
If you have a higher primary impedance, like 6.6k or 8k, a pair of 7591's should be able to take 550Vp and you'd probably need to reduce screen voltage a bit. I think the current requirements would be suitably reduced and the amp would put out probably 35W.
You'll need to measure the OT turns ratio and inform us of the speaker load options."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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EL37's? Astute choice ! ! Only problem - where in the sam hill are you gonna find them? Last I went looking for EL37, around 2001, there was some guy in Cyprus, selling one at a time for about $125 each. Plus shipping. From Cyprus for pete's sake... Probably military leftovers from postwar British occupation.Originally posted by Chuck H View Post
Granted, I haven't searched the interwebs, but I expect today's price would be somewhere north of $200 each. And I've never seen anybody making modern copies. Sure would be a treat if some outfit did go to the trouble, but I have a feeling they would be priced to the market, iow way more than 99.99% of musicians want to pay. Maybe suitable for some corque-snurfling high figh gighs.
Early Ampeg bass amps used EL37. Remember that company was founded by guys who were bass players and hi fi nuts, back in the late 1940's. Even back then, EL37s were no everyday item. I scrounged a couple out of ancient Ampegs, and they are indeed works of art, very hand built with tiny nuts & bolts inside, sort of a ship-in-a-bottle construction.This isn't the future I signed up for.Comment
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Im not an ee amp wizard like most people on MEF, can't offer a lot more than moral support, but you might get a strong mag light, and look carefully at every solder joint. A few around the tube sockets look like solder didn't 'wick' up the wire, and one ground on a big cap looks like it might be sitting there. (Might not be just due to angle of photo) Wouldn't hurt to look!
The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.Comment
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Yepper. I just looked into the probability of acquisition and discovered my faux pas (pinky outOriginally posted by Leo_Gnardo View Post
). The good news is that JJ is making a 7591 that is said to have the same voltage rating as the originals. If the primary impedance is low-ish, as it might be for a pair of el34's, there's still the option of doubling the speaker impedance to correct the reflected OT primary impedance for a pair of 7591's. I really think this could be a good solution.
"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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Thanks. Apologies for not remembering.Originally posted by Chuck H View Post
It was popular for PA amps of that era to run 6L6s at around 450V into an 8K load for 25W. Mismatch speakers and taps to get a 4K load, or run KT66s into 8K for a JTM45 thing.
Looking more at the photos, what I see is consistent with a JTM45 type circuit, except that there are two tubes wired up as plate loaded stage direct coupled to a cathode follower. Separate tone stack for each channel maybe? I think I count 9 pots in the photos. For sure there's a master volume or two.
Anyway, I'd plug in 6L6, EL34, KT66, 6P3S... There's enough bias range to accommodate any of them. And don't be afraid to connect an 8R speaker into the 16R tap. There aer schematics for the Heathkit A9 around that might help figure out which OT lead is which. Or it can be determined by experiment. Or maybe I would try them all and use the one(s) that I like the sound of.
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That's just how all lead free solder joints look! Seriously though, look at the build quality and organization, guy might not be a perfect soldering tech but looks well enough built to work first time. I think the Heathkit amp had 6l6gc, transformer may have had been used in more than 1 model.
I still say fill it up with tubes, bring it up on a variac while monitoring the B+, 6l6 will handle 500v.Comment
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7591's"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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Ive got it up and running. Pair of Sovtek 6550 in it. Voltage at the plates is 438vdc , bias is good . Interesting sounding amp..... awful high gain tones but back off the gain and its not bad .Comment
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From experience, I recommend replacing pertinax noval socket 2 and 3.
They knows can be not reliable, and after a long stand becomes the source of the problem.It's All Over NowComment
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What rectifier? What is the unloaded voltage with that rectifier? And what is your bias current? Please? I'm concerned that you have a pair of 40W tubes in there and the HV is loaded down 130V from last report!!! I'd just like to know that you're not exceeding the PT HV winding rating with the amp just sitting at idle. Plus, the 6550 draws another .1A each more filament current than even el34's so your filament winding is already over spec. Honestly, the 6550 is the last tube I would have chosen for that PT.I was proposing going the other direction with a lower wattage tube than the el34.Originally posted by Valvehead View Post"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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Home made amps are economical amplifiers made from cheap parts.
Every major investment adds to their unnecessary value, but it will still be home made.
At such amps changed only the most necessary parts to bring the amplifier to the correct state (output tubes, input (first) tube, potentiometer service)It's All Over NowComment
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^^^^^^^THIS^^^^^^^Originally posted by Chuck H View Post
I could not agree more.
Expect PT meltdown soon.Experience is something you get, just after you really needed it.Comment
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THe average plate current of one 6L6 in a 59 BM at full power (around 40W) is 80mA. Average screen current (2 tubes) is 17mA. Adding 10mA for the triodes makes a total DC current load of 187mA. Max. rms current of the HV winding needs to be higher than that.
Power tube current consumption drops with higher load impedance as does output power. The BM uses Rpp = 4.1k.- Own Opinions Only -Comment
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