Fender Hot Rod Deville blackface conversion

[MikePR]

Hi y'all:

With some Fender Hot Rod Deville Iron decide to make a single channel no reverb blackface head. Here is the work i have so far. Any input?

Thx

[sluckey]

Here are a few things that need attention...

Bias supply... You have a diode directly across the PT bias winding. Remove it or it will be destroyed when you apply power. If it shorts it will take out the PT also. The 22µF cap on the wiper of the bias pot is drawn backwards. Positive must go to ground.

V1B pin 6 has a 100K to ground. Remove that resistor.

V2B pin 7 must have a resistor to ground. V2B is gonna make this a high gain amp. I would eliminate V2 circuit completely (like the normal channel).

[eleventeen]

Looks pretty good, except I'm not sure what the purpose of V2 is. That tube (and you are only using half of it) *could* be used as an additional (variable) gain stage (meaning a "pre-gain" and "post gain" kind of topology) and I can assure you, a single triode gain stage inserted into the signal chain can make an astronomical difference in the type of amp it is....


I am referring to an AA763 non-reverb BF Deluxe which you can find in Doug's schem library. In that amp, the tube right after the tone controls (which we know we need bec the tone controls whack the signal a lot) feed DIRECTLY into the PI. In other words, if we lose one channel and we lose tremolo, that amp has 2 nine pin tubes and that's the end of it. Preamp > PI > 6V6.


Even an AA763 Bandmaster (driving 6L6 where maybe we'd think we need more voltage gain) does not have your V2)


If I was building the amp and wished for it to be an utterly stock BF amp, I imagine your V2 could be deleted. But I would find it very hard to resist punching out for a socket for that third tube even if this discussion leads you to believe that your V2 is not needed, in case I wished to hot-rod the amp later on.


Ed: Oops, Sluckey is right, remove the north-south bias rect diode

[MikePR]

Thanx for the input. Here is the latest fixed.

[2deaf]

There is a diode directly across the HT winding, also.

There is no feedback resistor.

An on/off switch might be handy.

[sluckey]

You really don't need the .047 and 220K that are connected to V1B pin 6.

Move the bottom HT lead to the junction of the bottom diodes to fix the error that 2deaf mentioned.

Add a 820Ω resistor in the NFB line.

[MikePR]

Wow thx. And i thought i did not miss anything. Version 3. 

[MikePR]

Does it look good now?

[sluckey]

The two resistors connected to the filament string should be 100Ω, not 100K.

How much voltage do you measure between the brown wires on the PT?

[MikePR]

72.5 vdc. And fixed the 100 ohm pilot light resistors,

[2deaf]

72.5 vdc. And fixed the 100 ohm pilot light resistors,

DC?

I am a little bit skeptical about the DeVille bias circuit giving acceptable voltages once the rest of the circuit on that winding has been eliminated.  If there is around 72V AC on the unloaded secondary, the attached standard bias circuit may be better.

[MikePR]

Thx

Here is the PT Specs:

40-18018

[sluckey]

Do you really have a Mercury Magnetics power transformer in this Deville? Regardless, I want to know "How much voltage do you measure between the brown wires on the PT?" I'm not interested in some dc voltage on a data sheet.

[MikePR]

53 VAC measured from brown to brown. PT is stock Fender one.

[2deaf]

Here is the PT Specs:  40-18018

Ah.  Now I see.  There is a voltage doubler using the center tap and one of the brown leads.  Your original two diode drawing would work if you use Brn/Yel and Brn as the leads and put the capacitor between the diodes and a lead.  Center tap to brown lead is shown as 28V AC on a Blues DeVille schematic.

[MikePR]

Can i use your bias schematic if i use brown to brown instead brown to Brown/yellow?

[sluckey]

53 VAC measured from brown to brown. PT is stock Fender one.

No need for a voltage doubler circuit. 53VAC is perfect for the simple bias circuit you show in your last schematic drawing. Although I prefer the circuit 2deaf posted. Connect one brown to the resistor. Connect the other brown to chassis ground.

Is this the same project you were working on back in August, September, and November of 2015?

[MikePR]

Yes the same one. Got busy at work and have to stop, also decide to go the simple way with no reverb route.

[2deaf]

Can i use your bias schematic if i use brown to brown instead brown to Brown/yellow?

No.  That was for 72V AC. 

You will probably have to remove the 51K resistor and maybe even change the 10K resistor to 4.7K in order to get -55V in the center of the range.

[MikePR]

Well guys I finished the Project but need help with 2 issues.

1) I want to lower B+ from 514v
2) Need a 60 hz hum eliminator circuit for it.
3) Any opinion to improve it is also welcome.

here are the schematics;

[sluckey]

B+ should decrease some if you bias it hotter. How is it biased now?

[PRR]

What is wrong with 514V on a 6L6GC amp??

There is ample B+ filtering. 60Hz hum is more likely heater wiring near sensitive audio points.