‘63 6G3 unpleasant overdrive issue

[MHProd]

My Deluxe seems to need some attention. The overdrive sounds pretty harsh, especially in the top end (not coming from the speaker).

The amp has grid stoppers and screen resistors. Electros are new.

In the PI, pin 6 has higher voltage than pin 1: 232v vs 229v, should be the other way around...

Everything else seems within range.

I also get -28v on both PI coupling cap... should I be reading negative voltage there? I know it’s normal where both 220k meet but also on the other side of those resistors?

[sluckey]

All those voltages, including negative voltages, are perfect.

[10thTx]

You could try a 10uf instead of 22uf on V1a cathode and a 5uf on V1b cathode. You could reduce the coupling caps between the LTPI and 6V6's to .047 instead of .1

With respect, 10thtx

[pdf64]

What is the context of this query, eg is this a newly acquired amp, or one you’ve had for a while that used to sound good?
If the latter, has anything external to the amp changed, eg guitar used, room / building it’s being used in?

[tubeswell]

Tube swap?

[Stevem]

On fender amps with .1 uf PI caps when they start to clip you can not run the same level of bass setting as when your playing with the volume at only 3 or less, as what might being made that your hearing is blocking distortion.

Either lower you Bass setting down and or as posted change those 2 caps to .47, or maybe even .22 and see how it sounds cranked.

You can also try out bypassing V1s second gain stage plate resistor with anywhere from a 250 pf cap to a 500 pf cap, you can also try the same with a cap going from the plate to the grid of that gain stage.
Make sure the caps have a 400 volt rating if you do this.

[Stevem]

Sorry about my post, those caps should be .047 uf or .022 uf.

[JD0x0]

Do you have the 100p across the PI for snubbing like the schematic?

Others have recommended reducing bass to prevent blocking. Do you hear blocking distortion? It can sometimes be harsh/fizzy and usually has some 'fart' or flub to it. Personally, I think either way, you could trim some bass. Fenders passed bass at uselessly low frequencies.

You could also try bypassing the NFB resistor with a cap to let more highs through in the NFB network, which will in turn roll off highs in the amp. (Basically the opposite of 'presence')
I usually run small snubbers on preamp stages to kill off hiss and harsh high frequencies and overtones.

[Faze]

What size snubbers would you suggest for a 6g3?

[NFG]

I am having a similar harsh overdrive issue with an AB763 Deluxe Reverb.
I have replaced several components, swapped tubes, (kept all originals
to reinstall after finding the problem); that is, I've replaced everything
except the rectifier tube, which in this case is a 5Y3, where the schematic
calls for a GZ34. My next move is to put in a GZ34 to see if that does it.

Were you able to resolve your overdrive issue?
Is there a 5Y3 in your amp?
Was the sound similar to a blown speaker?
I suspected the speaker at first.

Thanks

[Stevem]

In a DR if you do not have the higher output voltage by means of a 5AR5/ GZ34 or a 5U4 in the amp then your output tubes are idling too cold which makes for terrible sounding crossover distortion at almost any volume level if the amp has not been rebiased for that 5Y3 recto!

[NFG]

Okay, so what is the reason for using a 5Y3 in the DR?
Would it be best just to install a GZ34?
I have attempted bias adjustments, but can't get rid of the
annoying papery distortion.

Thanks for your reply

[Stevem]

Is this distortion at all volume levels?

If so unplug the speaker and plug in a set of headphones to fully rule out a bad speaker, you may also have a bad output transformer if the amp sounds like crap all the time/ at any volume level.

You also may have a open plate load resistor in the PI section.

[MHProd]

NFG, it sounds like our issue was similar.

My 6G3 had original its speaker and preamp tubes (1 RCA and 2 TungSol). The amp turned out to be ok for the most part. I upped the filtering a tad and installed grid stoppers on the power tubes to minimize high end oscillation. It helped a bit but not much.

After some time, I settled on an Eminence GA-SC64 which made the amp a lot warmer. I also spent quite some time tube rolling, tried different rectifiers too. I ended up putting TAD 6V6 in the amp (over a couple of NOS pairs) because they thickened the tone a bit. ALso changed the preamp tubes, NOS in v1 and v2 (can't remember what) and a JJ ECC83S in the PI.

All harshness is gone, the amp is loud, Volume on 6 and Tone on 8 with humbuckers = early ZZ Top in a box.