Penncrest SE 50C5 tube console amplifier

[happybear]

Penncrest AM/FM Phono console. The chassis was stripped and rebuilt as a SE tube stereo amplifier.

SE 50C5 beam power mode finals driven by a cap coupled 5751 twin triode.

SS diode rectified SS voltage doubler power supply with filter choke.

Tuned the loop FBK network to improve square wave appearance and transient response.

Added 10K ohm carbon comp grid stoppers to 5751 driving stage.

Schematics of signal circuit, power supply and standard measurements to follow.

happybear

 

[cademan]

Who built it? Those 50C5's are only good for about a watt of power output and those output transformers seem pretty big for the 50C5 transformers that are normal for that tube.

 

[zackthedog]

Nice job!

 

[happybear]

Who built it? Those 50C5's are only good for about a watt of power output and those output transformers seem pretty big for the 50C5 transformers that are normal for that tube.

Penncrest (Models # 7703A-46, 7704A-46, 7713A-48, 7734-48 per schematic). These were a J.C. Penny brand.

Per notes, 2W at clipping. Less than .8% THD @ 1W / 1KHz after rebuilding the circuit.

The chassis photo shows the power transformer and filter choke, the OPT's are mounted underneath and are similar in size to PT-31's.

Only paid about $10 for the console at a thrift store. Cost vs. performance is favorable.

happybear

 

[FlaCharlie]

The chassis photo shows the power transformer and filter choke, the OPT's are mounted underneath and are similar in size to PT-31's.

Only paid about $10 for the console at a thrift store. Cost vs. performance is favorable.

Can't beat a deal like that! I don't think I've ever seen a power transformer used in anything that has 50C5 outputs.

 

[cademan]

I know Pencrest. I meant who built this 50C5 amp out of a tuner receiver chassis?

What is your level of expertise? The 50C5 is a tube that doesn't need a power transformer and is more associated with a series string hot chassis design.

What kind of design is this frankenamp? Got a schematic?

 

[Mdpaudio]

I hope it’s not a line powered unit without a power transformer. Most of the 50C5 amps were in transformerless units that could fry you like bacon if they short out!

 

[Mike Stehr]

Kinda reminds me of Fleabreeze...

 

[cademan]

Thank you Mike. What an elegant way to use a series string tube and still be isolated from the mains.

 

[Mike Stehr]

The schematic is by Joe Rosen. If that schematic was ever conceived into a real circuit, I have no idea.

 

[happybear]

Penncrest Model # 7703A-46 per label on side of chassis.

Penncrest SE 50C5 stereo tube amplifier signal and power supply filter schematics by happybear.

Note: these circuits have been modified from the original schematics.

Currently listening on Altec 2-way horn system.

 

[gadget73]

Nice improvement on HF performance with the cap. All that ringing at 10khz is ugly.