Dano/Silvertone mystery

[mojo2001]

I picked up a Silvertone Danelectro 6L6 amp in non working condition. Speaker is shot.

Anyway, the B+ is 480V, which is in league of what would be expected for a 700vct power trans.

HOWEVER, looking at the schematic for this and other 6L6 15" Danelectros, I see that the B+ after the rectifier is indicated as the same or lower than 1/2 of the secondary AC voltage

In the attached schematic, we are to believe they are getting 320vdc out of a 680vct winding, cap input?

The power trans in mine might be a replacement...hard to tell.

Do Silvertone 1433s, Dano Challenger amps, and similar want 320V or 480V B+?

Which do I believe the B+ (leaning this way) or the transformer spec?

[guitician]

I guess it would depend on were two 12ax7 heaters in series with the cathodes of the 6l6's hold the bias. Running at 480v with all tubes installed? The C14 cap is only rated for 450v.

[mojo2001]

Yeah, two 12AX7 heaters serve as cathode resistance. 70V bias.

I put in a 475V Atom filter cap when I noticed the high voltage.

I am thinking this amp has a replaced transformer, changed to conform with schematic, and the B+ should actually be 320V.

Looked at other Dano 6L6 amps and they have the same odd low voltages coming out of high voltage transformers.

[guitician]

The max heater voltage for a 12xa7 heater is 13.9v. You should only have 27.8v Max at the cathodes. If you have a variac, you can see what B+ voltage that would correspond to. Of course you would want a "safe range" and run them at more like 24-25v.

[mojo2001]

Have a Variac but it it is storage. Just working my Fluke 8060A and a soldering iron at the moment.

I 'spect that adjusting with a variac to the B+ where I'll get 27v, the heater supplies will then be too low to light the tubes.

But I hear what you are saying. The voltage across those 12AX7 heaters is a reference point.

I think this amp wants 320V.

Maybe I should install an input choke then tune the voltage up to 320 with a small capacitor for "quasi-cap input."

Or, pony up for the proper power trans, once my suspicions are verified.

The other Danelectro amps I've used were pretty good, so I have high hopes for this box.

[guitician]

Oh, yes if your AC heaters are fine@6.3 then you've definitely got issues to work out. Do the heaters on the 12ax7 look too bright? Maybe a parallel dropping resistor would work.

[mojo2001]

Do the heaters on the 12ax7 look too bright?

Didn't look at that side of the amp while it was on...I was too occupied underneath waiting for the filter caps to explode!

[Enzo]

Is the B+ 480 with ALL the tubes in place? With no power tubes, the B+ will soar.

Are you using a real 5Y3 rectifier tube?

[mojo2001]

Yep, all tubes in place.

Real RCA 5y3, measuring 350V on each plate of the rectifier, 480 on the other side.

I think the transformer is wrong and I want 320. Contacting Edcor for a replacement.

Incedentally, the amp is not presently working with the 480V B+ but I can get ticks and pops though the OT by tapping the grids of the 6L6s.

Can anybody verify actual measured B+ on a Silvertone 1433, 1473, Dano Challenger or similar Dano 6L6 amp?