Old Rca Tubes!!!

[stompjunkie]

a buddy of mine has hooked me up with some awesome old RCA tubes. About half of them failed the test on my B+K, but enough have pulled through. Most of them test much better than the new tubes i've got laying around......Ok on to the real question.

There are a bunch of types I've never worked with before. I was wondering what I might be able to use in amps that I have and/or pieces I'm planning on building. I've been thinking about an octal preamp champ. Would I be able to replace the 6sc7 preamp with say a 6sl7, 6sq7, 6ac7, 6bl7, 12sq7, or 12sl7 ? Are 6k6 interchangable with 6v6? I know that some types of tubes are interchangable, but with diferent amplification such as 12ax7 and 12ay7... would the same principle apply here?

I've found some charts online, but everything so far has given names for 100% equivalents, and not a chart of what can be safely exchanged for different results.

Thanks for all the help!

[Andy Le Blanc]

hang on to those 6sl7 and 12sl7... and 6sn7 and 12sn7... they are becoming increasingly valuable as the NOS tubes become few....the 6k6 if I remember was intended for moderate power .....the design max plate voltage is 315....and application as a replacement for a 6v6 may not be the best....the 6k6 has a little more than half the plate dissapation of a 6v6....double check in any tube manual......and one way to increase the life of NOS tubes is to run the heater without any voltage on the plate for some time....it gives the getter...the thing inside that collects impurities in the vacuum tube .....a chance to do its job.... the tube should test better........

[muchxs]

6SL7 is an easy swap for 6SC7, just re-wire at the socket. You want the elements to be wired correctly, plate wiring to plate wiring, grid to grid, filament to filament, etc.

6SQ7 / 12SQ7 is a hi-mu triode / double diode. Use the 6SQ7 where you need an extra gain stage, ignore the diodes. It's similar to miniature type 12AV6 or 12AT6. The 12SQ7 is semi-useless unless you have a 12 volt filament supply available.

If you find a good application for the 6AC7 I'd like to hear about it, I have a couple hundred 6AC7s.

6V6s are inexpensive enough, use a 6V6 where you need a 6V6 and save the 6K6 for old Fender reverbs.

[skyboltone]

Also, check carefully the notes on the B&K. For instance, my B&K says a 30% test is full factory spec on a 12AX7. Some of your tubes may actually be ok, they just don't test in the green.

[stompjunkie]

Thanks guys! That helps alot.... yeah, I've had to be really carefull with the tester, checking through all of the little notes.... I've given him back quite a few of the tubes that I can't use, and he'll probably sell them. I couldn't just take all of that $, though I gave him some cash for what I've kept.... I can't wait to build some more and put these to use!

Thanks again!

[Tubetwang]

As a side note them 6G15 Fender Reverb may be used as a 1 watt amp.

[v846]

Also, check carefully the notes on the B&K. For instance, my B&K says a 30% test is full factory spec on a 12AX7. Some of your tubes may actually be ok, they just don't test in the green.

Ditto that, I would probably hang on to any 12AX7 that passes shorts & emissions on a B&K tester especially the 700 series..

[skyboltone]

Also, check carefully the notes on the B&K. For instance, my B&K says a 30% test is full factory spec on a 12AX7. Some of your tubes may actually be ok, they just don't test in the green.

Ditto that, I would probably hang on to any 12AX7 that passes shorts & emissions on a B&K tester especially the 700 series..

I wasn't going to admit this. It's about the saddest tale you'll ever hear. I got hold of an old Concord tape recorder and it had one dozen Telefunken 12AX7 that all tested at 30%. I chucked them all in the trash. This was about 15 years ago. I still wake up in a cold sweat over it.

[v846]

I wasn't going to admit this. It's about the saddest tale you'll ever hear. I got hold of an old Concord tape recorder and it had one dozen Telefunken 12AX7 that all tested at 30%. I chucked them all in the trash. This was about 15 years ago. I still wake up in a cold sweat over it.

Ouch...I saw someone refer to tube testers as electronic Ouija boards
interesting read concerning B&K's
http://www.antiqueradios.com/forums/vie ... ight=12ax7


stompjunkie,
What model B&K ,calibrated ?

[Structo]

Yes, I remember going to the grocery store with dad when I was a kid.
Seemed like everywhere had a tube tester from the grocery to the drugstore.
Man I wish I had the tubes that those old testers had stored in the bottom cabinet....

[skyboltone]

I wasn't going to admit this. It's about the saddest tale you'll ever hear. I got hold of an old Concord tape recorder and it had one dozen Telefunken 12AX7 that all tested at 30%. I chucked them all in the trash. This was about 15 years ago. I still wake up in a cold sweat over it.

Ouch...I saw someone refer to tube testers as electronic Ouija boards
interesting read concerning B&K's
http://www.antiqueradios.com/forums/vie ... ight=12ax7


stompjunkie,
What model B&K ,calibrated ?

I'll have to take a look at the model. I forget. I think 600 series. It's got octals inside. Calibration is something I've never looked into because It's got unmarked resistor banks and I've not found a schematic.

Anyway, 6EA8s test weird too but I don't play with them much anymore having gotten out of radio. The only thing I use the tester for is searching for shorts and gas. Otherwise I'll listen to it. I also don't throw any tubes away no matter what anymore.

[v846]

The 700 & 707 are easy to cal,not familiar with the 600 series but I'm guessing they're not much different than the 700...
Ya might find the schematic at bama

http://bama.edebris.com/manuals/

[stompjunkie]

Thats an interesting link.....it's a 707. It's been calibrated recently, and it's also been re-capped...... I don't trust it 100%, but so far I think it's pretty accurate....Thats sad to hear skybolt...but you live and learn....I know I have