Conn organ amp to Vibrolux 6G11. in over my head!!

[zapped]

Trying to convert Conn power amp to single channel (bright with trem.) Fender 6G11. Could not find schem. online for the Conn. Its a 2x6L6GC, 5U4gb, 6DN7, 6S4, Oc2 12AX7 tube unit. Had a cap. can with 2x40uf x 500v. Goal was 2x6L6GC and 3x 12AX7's. Used the multi cap from Doug w/ 40, 20, 20, 20 @500v wired like the 6G11 schem. Problem is voltage seems too high. PT reads 425-0-425 no load no recto. tube. With 5U4GB recto. I get 570 vdc to power supply and with GZ34 I get 580vdc. I stopped before the capacitor failed. Question did Conn use voltage this high for 6L6's normally? Thanks Ed

[sluckey]

Plug the 6L6s in and see how much the B+ drops.

[Paul1453]

Did you have all the tubes in when you took your voltage readings?
I made the mistake of checking voltages without all the other tubes in before,
and got too high voltage readings myself.   

With all the tubes in the voltages were right in line with expected readings. 

Sluckey did set me straight then too.

[zapped]

Thanks Slucky. With 6l6's installed voltage went to 538vdc. Tubes seemed very bright.

[sluckey]

I'd be nervous with 500v filter caps.

[zapped]

Can a big resistor on the Secondary center leg of PT be used to lower the voltage ?

[sluckey]

Yes, but you have such a loooong way to go to get down to 6G11 voltages.

[dude]

 Your PT is too big. You need to drop a lot of volts, Zeners, Power Resistors can be used but the values would be on the high side, too much voltage to drop, IMO, I would get another PT with maybe 325-0-325.


See who else chimes in.


al

[zapped]

The PT, recto, power tubes and power supply are close to original, so could that be the voltage Conn used it seems too high for any 6l6's??

[mresistor]

The Conn organ was probably designed to run on 110vac or 115vac and now that you have 120vac + line voltage input, this makes the secondary much higher. I used diodes on the center tap to lower my high volts but not nearly as many volts as you need to drop.

[Paul1453]

I think the original Conn organ probably ran the plates of the 6L6GCs at +450 VDC.
That seems very common for 6L6GCs and fits with the 500V cap can.

I didn't look at what the 6G11 uses for B+,
but if it is +400V or less, this PT may be a little too hot for it.   

[mresistor]

6G11 6L6 plates running at +365.   I'd also agree that you need a different PT.   


like this one maybe  http://www.ebay.com/itm/PT275-2-USA-POWER-TRANSFORMER-TUBE-AUDIO-275-0-275-x100mA-/161905036341?hash=item25b24acc35:g:tS4AAOxynLhR~wBI

[zapped]

Just noticed I posted under the wrong topic. Thanks for moving it to the correct place Steve.

[zapped]

Thanks for advise. I'm really a hack at this and most of the theory is above my tech. level. My one observation based on some of the posts I've read is a small output transformer would yield less output watts. This unit seemed to have a small output transformer ( much smaller than the Stancor I used for a 5E3 build ) for a 2 x 6L6GC amp running at near 500 volts. Without the schematic and using the 500v rating from the original power supply caps. I thought it would be close enough.. Oops. I assume the entire 6G11 circuit was designed around the 365v B+ .  Thanks again for all the help..   Ed

[zapped]

Update: I've replaced the OT with one from a Seburg juke box power amp. the pushed 2 x 6L6g's. 325-0-325v. it gives me about 396v. from the 5u4gb. Next problem is motorboating above 1/4 volume. When recording voltages V2 pins 1,7 & 8 were cycling 120 -230 volts. Is that normal? I'm sure there are other Gremlins to shake out but this seems like the biggest..I recorded all voltages in the voltage page on this forum but could not attach it to this post. Thanks  Ed

[sluckey]

Motorboating is usually filter caps or poor ground somewhere, possibly a grid return circuit.

What function does V2 serve in your amp? If it's the tremolo circuit then voltages would be changing at the trem rate if it's working.

We need to see your as built schematic.

[zapped]

I used the fender schematic for 6G11 and one of Doug's boards with the norm channel sawed off so yes V2 is for tremolo. I used the JJ multi cap 40,20,20,20 @ 500v. for power supply. The trem. works when the intensity is turned up. I guess the foot switch when grounded cancels the trem.? http://el34world.com/charts/valve/ValveData.php?e=view&f=19291