50's rca s e amp project

[tominredbank]

I recently acquired this little rca amp . Works great. I want to replace all the caps and resistors and give it a new home in a custom case. Can anyone see from my photos how to remove the amp from the tone controls/volume control section? I'd like to run it into an outboard preamp. Those 4 wires to the left were my temporary cd inputs. Also there are a resistor and cap on each input from factory. Were they to compansate for the ceramic cartridge? Do they stay? Thanks,,,,tom

 

[cademan]

Take a look at the 6EU7 data sheets.
http://www.mif.pg.gda.pl/homepages/frank/sheets/049/6/6EU7.pdf

If you want to bypass all controls and just have a straight power amp driven by a separate preamp, then you will want to change the left & right RCA inputs to go straight to pins 5 & 8 respectively.

 

[Tom Bavis]

3VE07 isn't listed in Sams - is there a number "RS-xxx" on the chassis?

 

[tominredbank]

On chassis: RS193D also 2066L7

 

[tominredbank]

Pin #5 on one 6bq5 and #8 on the other? Do I eliminate the resistor and cap on each channel just inside the Molex?

 

[cademan]

Pin #5 on one 6bq5 and #8 on the other? Do I eliminate the resistor and cap on each channel just inside the Molex?

NO, NOT the 6BQ5 tubes, but the single 6EU7 tube. The 6EU7 is the input preamp tube and is a dual triode in a single envelope. This means that one triode inside the 6EU7 drives one of the 6BQ5 tubes. The other triode drives the other 6BQ5 tube.

If you want to bypass the volume and tone controls, then do what I suggested previously. The left RCA input will need to be connected directly to pin #5 of the 6EU7, and the right RCA input will need to be connected directly to pin #8 on the same 6EU7 tube. This will then effectively bypass any and all controls and make it a straight power amplifier.

 

[tominredbank]

Thank you. After I read my last post and looked at the amp I realized how dumb that was for me to say. Also on the 6bq5`s at pins #2 there is a resistor going into the " tone control " wiring. Remove that too I imagine? Thanks

 

[knockbill]

Yep, 193 amp... I rebuilt one and gave it to a friend,,, got him into tubes!!

 

[Tom Bavis]

Here's a schematic

 

[tominredbank]

Thaks Tom

 

[tominredbank]

On my RCA the only part now I don`t understand is pin#2 on the 6bq5`s. On one #2 leads to a resistor and into I believe the balance control and on the other #2 to a resistor, then pin#8 on the 6eu7 and finally to ground. Anyone have an idea how I terminate them to use the RCA as strictly a power amp?

 

[BinaryMike]

It should work as a straight power amp if you just short out R207/R209 and set the controls as follows:

Bass: full CCW
Treble: full CW
Volume: full CW
Balance: center

It wouldn't hurt to clip R222 out as well. Sensitivity might be excessive. Post here if so.

 

[tominredbank]

Thanks Mike but my goal was to physically eliminate the tone / volume / balance section altogether.Pin #2 6bq5 goes to resistor then ( i think) balance pot. Other 6bq5 #2 pin to resistor , pin#8 on 6eu7 and to ground. Any ideas?

 

[tominredbank]

Ooops! Correction please. One 6bq5 # 2 pin to resistor then to one of the tone controls, the OTHER # 2 pins to resistor and to pin #3 on the 6eu7. My age my eyes.

 

[knockbill]

Pins 5 and 8 are the grids of the input triode,,,if you inject a signal there, it will eliminate the bass/treble pots,,, the .047 caps are the coupling caps jump to #2 pins on output tubes will bypass the Vol/Bal... try it with jumpers first...

 

[tominredbank]

Thanks. Let me run through it to be sure. Left input to pin 5 on 6eu7. Right channel input to pin 8 on 6eu7. Left and right coupling caps to pin 2 on each 6bq5. Do the resistors stay which are coming off pins 2 on the 6bq5's now?

 

[knockbill]

I think I read the numbers correctly,,, the schem gets distorted if its blown up too much... just connect to the grids,,, I think the resistors are part of loud/bal ckt,, that's why I said try em with jumpers first, and see how it passes the signal thru the amp stages... You can put a cap on the test jumper before the grid if there isn't one in the ckt...

 

[tominredbank]

Thanks. I'll give it a shot maybe tonight after work

 

[macyjrm]

You're gonna be happy with the outcome. Here's a pic of mine running at night adjacent to my back yard fire pit. Using an Advent 300 in preamp mode. Tone controls removed. Lots of fun, sounds great.

 

[nj pheonix]

I guess I scared you off with the technobabble in the PM.
I'm still available if you get stuck