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Old 7th April 2013, 09:15 PM   #1
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Default NOOB ALERT! sooo omany questions.....

Hi everyone!

I recently came across a cache of old vacuum tubes. Most look used.. A few are in boxes. I have a feeling that most of them are from televisions and old home audio stuff. I have been able to identify a few of them. ( I have a '69 Bandmaster Reverb) But.. danged if I know if any of them are working .. I was wondering if perhaps there may be a member ( with a tester) close to the Sacramento area who might be willing to meet with me and give me a hand finding out if any of these things are working and worth anything for say a .. few choice tubes or a 12 pk or somethin?? I have pictures I can upload to photobucket if that would help

Ben ( Davis CA)
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Old 8th April 2013, 12:47 AM   #2
DUG is offline DUG  Canada
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You might sell them as-is.

Put up a list...If the tubes are not wanted then you don't need to use your time to test them.

Just a suggestion.

Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
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Old 8th April 2013, 10:07 PM   #3
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That's just one question...
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Old 18th April 2013, 04:07 AM   #4
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rightyo! Funk1980! The other question is what happens if I pop a 12BH7A into a spot on my 1969 Fender BandMaster Reverb that is supposed to have a 12AT7 in it?
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Old 18th April 2013, 06:29 AM   #5
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Putting a 12BH7A in place of a 12AT7 in fact would not be too serious, more by luck than anything else. In this particular case the pin outs match, same heater wiring etc. but just stuffing any tube in any tube socket just because it fits is "fraught".

The 12BH7A however would not run at the operating point expected by the Bandmaster. And would probably sound pretty awful.

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Old 18th April 2013, 06:34 AM   #6
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WEEEEEELLLLLLLLLLL.. I did it.. turns out.. sounds freaking awesome! its a much darker tone.. I dont get the distortion at high volumes but other than that its pretty freaking sweet! It wasnt just any old tube really.. a dual triode instead of a twin triode. right?
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Old 18th April 2013, 11:29 AM   #7
DF96 is offline DF96  England
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Dual triode = twin triode. Two names, same thing.

If swapping a valve for a quite different valve (which happens to have the same pinout) 'improves' the sound then either the circuit was badly designed for the first valve or the listener prefers the distortion introduced by the second valve. You choose.
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Old 18th April 2013, 01:24 PM   #8
godfrey is offline godfrey  South Africa
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Dude, it's a guitar amp! They're supposed to be "badly designed". You think musicians want low distortion?
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Old 18th April 2013, 01:47 PM   #9
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Not to mention the 12BH7 draws twice the heater current from the PSU compared tot the 12AT7. Are you sure it's up to it?
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Old 18th April 2013, 02:24 PM   #10
GoatGuy is offline GoatGuy  United States
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Oddly [DF96] enough ... a musician friend had a similar experience, except with the 12BZ7 tube, again pinout-compatible with the venerable AX7. He asked "is this OK to do?", and taking a look at his amp, I confirmed it had a stout heater, and the usual resistor-capacitor bypass on the front end, so it was a go.

And the sound definitely got "darker", less distorted at the top (which for guitar players is a bug, not a feature, mostly), but in the middle region, was darn sweet. Very jazzy. So... some 5 years later, the 12BZ7 has been replaced ceremonially to show people, but it remains in the box for the gigs.

As to double-the-heater-current, we're not talking about serious current: the overall power draw (line tubes, phase inverter, push-pull 4-tube final) might increase 5%, maybe less. Clearly within design spec.

I highly recommend experimenting with these "front end tubes" in guitar amps. Just be sure that the whole amp is tube based, and not one of the dumb modern ones with a single 12ax7 (typically behind a cute orange LED backlit or underlit window!) in the front end, and all silicon after that. The double-amp heaters might well be way beyond that capacity of the design! Only ALL TUBE is safe.

12AU7, 12AT7, 12AY7, 12BH7, 12BZ7 ... all good, different gain! Its especially fun to try different manufacturers' substitutes - comparing the Ruskies to the Chinee, to the German's NOS (since the make them no more). The front-end tube of the guitar amplifier has one of the most significant roles in "sound shaping" of any of the tubes.

Have fun!

Also check out the "franks tube pages" sites. It is NOT easy to find all the substitutes, but with some scanning and a pad of paper, you will locate 50 or so different types to give you stuff to try.

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