AO-43 to Gibson Tweed RVT

[vampwizzard]

that had no effect on the oscillation.

[vampwizzard]

I replaced the choke with a 470K resistor and that also did not change the situation.

[vampwizzard]

Updates: volume/tone was wired incorrectly. I took the trem triode off its B+ node and have a functioning and very satisfying amp. When I reattach the trem circuit to B+ the oscillation returns, but now its controllable by the tremolo speed control but not depth. going to look into how I wired that trem circuit up.

[vampwizzard]

more updates: disconnected the trem circuit and added reverb in. The reverb was absolutely fantastic.. its a really good sounding circuit.

However, started experiencing overheating through the 250K 10W voltage dropping resistor added from the rect B+ to node A. Ill check voltages again tomorrow.

[vampwizzard]

Some odd problems.

Took the voltage dropping resistor off the B+ pre node A on the filter cap. With all tubes installed my B+ is 270 with a 5Y3. The soldered connections were all reflowed and checked.

I have one 6v6 that gets hot and blue's up and it does so in either position. The low voltage is killing my bias.. 16W and 19W respectively. Obviously not keen to turn it back on.

Another oddity is that one leg of my OT measures 184 Ohms to center and the other 211. Is it normal to have them 15% off from each other?

[shooter]

I call the ohms normal
the 6V6, not.
blue isn't so much a problem, increased current is

[ac427v]

You have made a lot of changes. I've lost track of what the circuit looks like with the power supply change. Can you update your schematic for us? and include the bias circuit and show where you disconnected the trem? Of course, I would love to see the final implementation of that reverb too! I'm always looking for something new to try.

[vampwizzard]

You have made a lot of changes. I've lost track of what the circuit looks like with the power supply change. Can you update your schematic for us? and include the bias circuit and show where you disconnected the trem? Of course, I would love to see the final implementation of that reverb too! I'm always looking for something new to try.

The only change from the original schematic is the trem B+ is removed and the first 22K dropping resistor is a 10K. EDIT: the insertion node off the pot is also removed. it is detached from the overall circuit.

See attached.

[vampwizzard]

I call the ohms normal
the 6V6, not.
blue isn't so much a problem, increased current is

I usually get this backwards when dealing with resistors on the ground circuit. More resistance for my cathode bias resistor will drop current and raise voltage, correct? Id go from a 250ohm to 450 or 500 whatever ive got kicking around.

[shooter]

More resistance for my cathode bias resistor will drop current and raise voltage

Yes
BUT
If you have a bad 6V6, that's just cheating 
get measurements with current tubes at idle, then swap in a "new" tube for the gassy one, recheck.
otherwise, add R til you get "in spec"

[vampwizzard]

thanks! ill update after I get the parts in.. all of my backup power resistors are either 1k or 150ohm. plus waiting on new tubes.

Now to think of a use for this single 6v6.. hmm... lol

[shooter]

to think of a use for this single 6v6

put it in a box labeled "shop spare", that way next time you don't have to wait on parts 

[vampwizzard]

Alright. 470ohm got me where i needed to be. As built schematic attached. I need to do some tweaking on the reverb circuit.. once i get above 2 or 3 (out of 10) I get a really harsh high frequency noise. Otherwise she sounds pretty sweet. One error is that I didnt attach the grid leaks back to ground after removing the trem and that probably fried that power tube.

[sluckey]

R9 and R11 are usually the same value. The values you used will cause a big difference in drive voltage to the 6V6s.

[vampwizzard]

R9 and R11 are usually the same value. The values you used will cause a big difference in drive voltage to the 6V6s.

Thank makes a lot of sense. A 56K for the load resistor (R9) would be more in line with the GA18T. Should I look to replace R9 to that value?

[sluckey]

GA18T uses 100Ks, but GA19RVT uses 47Ks. The important thing is for both resistors to be the same value.

     https://el34world.com/charts/Schematics/files/Gibson/Gibson_ga_18t.pdf

     https://el34world.com/charts/Schematics/files/Gibson/Gibson_ga_19rvt.pdf

[vampwizzard]

The wonderful world of gibson amps.. theres different schematics with poor revisioning history. Heres the G18T i was referring to.. a bit more like the GA19RVT. Ill get that changed over. Thank you.

http://djlservice.com/GibsonGA18wPhotos_files/image014.jpg

[shooter]

theres different schematics with poor revisioning history

 

work on them long enough, you get a pretty good idea what happened at lunch 

[sluckey]

Even worse... It seems that during the actual assembly if the 'normally' used component was not handy, the worker just grabbed something else.