12AX7,6BQ5 PP Amp Search.

[Troncones]

I looking for an amp model that uses these tubes. The schematic needs to be available at Sams or ?.

[TheGimp]

Guitar Amp? Stereo Amp? SE? PP?

What are you wanting to do? Build an amp from a schemtic?

There are lots of old tube amp designs (Grundig EL 90, Telefunken EL90, Dynaco ST-35 12BQ5) out on the internet.

Scroll down to the bottom and look at the Harmon Kardon amps here for example.

Wade's Audio And Tube Page

Or here, but they don't say which tubes in the description, you will just have to open the schematics and look to see what tubes they use. 6BQ5 will be in the 4-6W range for SE and 8-12W range for PP.

Consumer Audio Information

[Frank Berry]

You can start here. The 6V6 tube has the same specs as the 6BQ5.
Audio Electronics Page

[Troncones]

Thanks everybody. Sorry, stereo amp. I have a Zenith chassis that uses 12AU7's and requires a preamp. Instead of building the preamp section I thought I would keep it simple and repalce the 12AU7's with a high mue twin triode. I'm not at the skill level required to design from scratch so I was looking to build something to a proven design.

[TheGimp]

If you could post a schematic I'm sure you would get some more detailed advise as to how feasible this would be.

[vinylkid58]

Originally Posted by Troncones

Thanks everybody. Sorry, stereo amp. I have a Zenith chassis that uses 12AU7's and requires a preamp. Instead of building the preamp section I thought I would keep it simple and repalce the 12AU7's with a high mue twin triode. I'm not at the skill level required to design from scratch so I was looking to build something to a proven design.

Sounds like the perfect opportunity to build an "El Cheapo" variant, just without the 12AX7's.

http://homepage.mac.com/planet10/for...3jun06-map.gif

Jeff

[nigelwright7557]

Originally Posted by Troncones

Thanks everybody. Sorry, stereo amp. I have a Zenith chassis that uses 12AU7's and requires a preamp. Instead of building the preamp section I thought I would keep it simple and repalce the 12AU7's with a high mue twin triode. I'm not at the skill level required to design from scratch so I was looking to build something to a proven design.

A 12AX7 has a higher mu and is pin for pin compatible.

[Eli Duttman]

I'd love to see the Zenith carcass turned into an "El Cheapo" variant, but PSU considerations are likely to make the idea a non-starter.

Zenith was the last company to abandon P2P wiring in favor of PCBs and I expect the chassis is hand wired. If it is PCB, tweaking becomes problematic.

Implicit in the OP's remarks is the use of a passive control center, along with the likelihood that the amp came out of a console. The PSUs in console amps frequently supplied tuners and preamps too. I say use Dyna SCA35 style, with 6U8s in the small signal circuitry. 7199s have become "unobtainium". If the Zenith O/P trafos lack UL taps, use full pentode mode and regulate screen grid B+ at 250 VDC. The little LR8 IC seems well suited to this task. The SCA35's pentode voltage amplifier safely allows 470 KOhm grid to ground resistors. That means 50 KOhm pots. are OK in the passive control center. Just keep the connecting cables short and low capacitance.

Oh yeah, definitely use separate RC bias networks in each channel. Tightly matched pairs are much easier to source and cost less than good quads.

[Eli Duttman]

Originally Posted by Frank Berry

You can start here. The 6V6 tube has the same specs as the 6BQ5.
Audio Electronics Page

Not so, the 6V6 and 6BQ5 are electrically different. However, O/P trafos used with 1 of the 2 work just fine with the other.

[kevinkr]

Is the amplifier in question an SE amplifier with a single 12AU7A and a pair of 6BQ5? Or PP with two 12AU7A and four 6BQ5? Most console amps I have run across using 6BQ5 have been SE, but not all.

A 12AU7A/6BQ5 based SE amplifier should have enough gain for most line level sources without major modification..