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Economy push pull audio output tubes
Economy push pull audio output tubes
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Old 28th October 2017, 04:29 PM   #1
LSR is offline LSR
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Default Economy push pull audio output tubes

I am looking to marry an existing preamp that I feel sounds good, to a push pull power amp of modest output. I'm speaking of guitar amps here. I want to use some of the easily procured small bottle output tubes found in the mass produced sets of the day. So rather than buy batches of each one, test various configurations etc. I am hoping that someone here has hands on experience with the various 25(a,b,c), 30(a,b,c) 35's,50's etc. Specifically, help me save a bit of money, and alot of time by suggesting where to start looking for the better sounding ones. Also, if any known consistency issues. I had come across a site about 10 years ago but can't remember where. Perhaps we've a few old school or that could help? Cathode voltage is not an issue.
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Old 28th October 2017, 06:12 PM   #2
Enzo is offline Enzo  United States
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There are only so many tube types readily available and likely to be around. As for small, EL84 and 6V6 are your main choices.

I don't know what you mean with 25s, 30s, 35s, and 50s, unless you mean power amp output levels. The difference between them is negligible. All else equal, 50 watts is only 3db louder than 25 watts. There are any number of existing circuits using a pair of EL84, or a quad. And a pair of 6V6 is the basis of the classic Deluxe Reverb by Fender.
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Old 28th October 2017, 06:15 PM   #3
leadbelly is offline leadbelly  Canada
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He means tube numbers, as in really old radio set tubes. It's an odd request. I can't for the life see the reason other than an intellectual exercise.
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Old 28th October 2017, 06:43 PM   #4
kevinkr is offline kevinkr  United States
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Economy push pull audio output tubes
What is your power target? Modest is undefinable. Some of the types you've mentioned are quite rare, and extremely expensive.

A single pair of 6BQ5 might be a realistic alternative, if you want dhts which seems to be the case from the types you mention perhaps a pair of 45s would do the job? (It's not very likely that any of the types you mention would have found their way into instrument amps in any significant way as they are a bit early.)
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Old 28th October 2017, 06:52 PM   #5
Tubelab_com is offline Tubelab_com  United States
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While I have played my guitar through a DHT amp and do like the unique tone. DHT's do not work for anything that gets lugged around and banged on.

As an exercise in insanity a dozen years or so, I put my 845SE amp in the trunk of my Ford Mustang, and plugged it into a power inverter. The fine details of a DHT amp are lost when sitting in a traffic jam in a convertible, and the filament in one of the 845's died from too many trips down a bumpy road.

Any DHT that is over 50 years old must be treated with care.
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Old 28th October 2017, 07:37 PM   #6
Printer2 is offline Printer2  Canada
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A said, what is modest output? 1W, 5W, 10W, 20W? I am guessing you are asking in the 5-10W range, the one watt thing has been extensively mined with the 12AU7 even though I think using a pair of 6AK5's is the better choice. I have a pair of 35L6's with transformer that came out of a radio which would make a nifty 6W amp rather than going single ended with a 6V6. While we are in the range there is the 6AQ5 which will make up to 8W in P-P, still cheap to buy and you don't have to do anything odd to use them, any 6V6 circuit but with reduced voltage. Not a lot cheaper but there is the 8 pin family of 12L6's, 12W6, 25L6, 50L6. About the same price as the 6AQ5's and power output.

Then there is the 12V6, might not be cheap as the above tubes but you can get them at reasonable cost. Use them in their spec sheet limits or below and you might never need to buy a second pair again. The odd pin or voltage versions of the EL84 is out there also. A quick search will get you more information.

You do not say what you are planing on using for HV supply or output iron, can make a bigger dent in the wallet than the tubes. What cathode voltage has to do with things I don't know.
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Old 29th October 2017, 01:08 AM   #7
Tubelab_com is offline Tubelab_com  United States
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Quote:
What cathode voltage has to do with things I don't know.
When I first read this post it didn't make sense to me. then someone suggested that the 25, 30, 35 and 50 thing meant DHT's. But the thread title used the word economy, which doesn't jive with DHT. Power output maybe? By my standards any of these would be considered modest power output ratings. My guess on "cathode voltage" is heater voltage, and all of those numbers except maybe 30 fit that too.

Quote:
family of 12L6's, 12W6, 25L6, 50L6. About the same price as the 6AQ5's and power output.
You don't want to know how much power I can squeeze out of these guys without melting them. Look at the data sheets, both the curves and Class A1 amplifier characteristics match, however the maximum plate voltage spec for the xxL6's is 200 volts, while the max plate voltage spec for the 'W6 is 300 volts. So if everything else is the same, why can't you feed a 25L6 say 300 volts......well you can. So if 300 volts works, how far can you turn the knob. Well I ran out of knob on my little 400 volt supply, so I hooked up a bigger one. All of these tubes can eat over 400 volts, Some tend to run away around 450 volts, or you can't run enough bias current to fix crossover distortion without melting the tube, but 40 watts from a pair on 300 volts works without any hint of redness, so make a 30 watt amp on 350 volts, and it will last.

There are at least two more members of this family that I won't mention here because they will disappear. PM me if you want the numbers. They have the same internals, same curves and characteristics, but smaller plates with smaller dissipation ratings to fit in smaller bottles.

Quote:
Then there is the 12V6, might not be cheap as the above
The 12V6 can be found for $4, and it's 9 pin equivalent the 12AB5 is $3. 20 to 25 watts can be squeezed out of them if you bend the plate voltage spec a bit.

Quote:
The odd pin or voltage versions of the EL84 is out there also.
Some of the xxL84's are not odd voltage EL84's. The PL84 and UL84 are odd voltage 6CW5's. They will crank out 25 watts per pair if you run the screen grid at 150 volts or so. Dropping them into an EL84 circuit with more than 200 volts on the screen is an instant meltdown.

There are plenty of common TV tubes, or old radio tubes that can be used to make a guitar amplifier, but more information is needed to figure out what is being asked for here. How much power?
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Old 29th October 2017, 01:28 AM   #8
kevinkr is offline kevinkr  United States
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Economy push pull audio output tubes
Maybe he is talking about series string tubes like 25C5, 25L5, 50L5 and 50C5? Would be helpful if he spelled it out a bit more clearly.

Until and if the OP weighs in I guess we won't know exactly.

I would probably choose the 6AQ5/6002 over the list above.

I worry that he may be thinking of a very "economical" amp sans power transformer and hence the interest in these tubes?
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Old 29th October 2017, 01:51 AM   #9
Tubelab_com is offline Tubelab_com  United States
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It would also help to know what his existing preamp needs, 6V or 12V heater tubes, solid state?

Quote:
very "economical" amp sans power transformer and hence the interest in these tubes?
That is a SHOCKING thought. I have determined that the series heater tubes can be used to make the cheapest possible guitar amp INCLUDING the cost of an isolation transformer, but this won't work if the existing preamp uses parallel wired 12AX7's, or need +/- 15 volts to feed opamps.
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Old 29th October 2017, 03:19 AM   #10
Printer2 is offline Printer2  Canada
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Pretty much know that you could get more out of the tubes than they are rated for George, even thought to mention you and the idea of modest power starts around 50W. From the OP's requirements it seems he might not have your disregard for seeing a little smoke. I would take a crack at seeing how much I could get out of some of those tubes one day, just not enough time to play around.
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