Proposed 18W variations - sanity check?

[Lectroid]

Decided my next build will be the Hoffman Stout Reverb, based on the Marshall 18W but I'd like to use a different PT that I currently have on hand.  Can I do this without changing the character (or resulting audio performance) of the original circuit?  With my existing PT, I can

1) Use a 5Y3 or other 5-volt rectifier instead of the 6V EZ81, or even go with SS rectification
OR
2) Should I plan to use one of the '18W' PTs being sold around, like Mojotone's Heyboer? 

I know the  SS rectification will sound tighter than with tube rectification.  Anyone have an opinion on whether that will degrade the sound of a stock 18W circuit?

I will use 'std' OT for the 18W, probably the Hammond 1750PA?

No other changes are planned.

Thanks for your help.

[sluckey]

Decided my next build will be the Hoffman Stout Reverb, based on the Marshall 18W but I'd like to use a different PT that I currently have on hand.

Need more info. The 18W amp likes a 290-0-290 high voltage winding.

Since you have a 5V winding you could do a 5Y3. But since you must also have a 6.3v winding, you could do an EZ81. Your choice. I have 18W EL84 amps that use a 5Y3 and some that use an EL84. Both sound fine to me.

[Lectroid]

Your choice. I have 18W EL84 amps that use a 5Y3 and some that use an EL84. Both sound fine to me.

'...some that use an EL84.'  I'll assume you meant EZ81.  Thanks for clearing that up--I don't want to lose any Marshall mojo just to save a few bucks.

Need more info. The 18W amp likes a 290-0-290 high voltage winding.

What is the max voltage I should put on my 6BQ5's in your opinion?  I think my candidate PT will put around 310V on the 6BQ5s.  Can I get away with 310V?  On your November project it looks like the plates of the EL84s are getting 348V.

And have you ever tried the mod of replacing the R14 470K resistor on V3-B with a 500K pot as a 'Gain' control as it shows on the schematic?

Ref:  https://el34world.com/Hoffman/files/Hoffman_StoutReverb.pdf

Thanks again!

[pdf64]

…
Ref:  https://el34world.com/Hoffman/files/Hoffman_StoutReverb.pdf

The phase splitter looks wonky, the grid of the common grid section isn’t decoupled.
The LTP would probably operate better if the cap was ‘grid to common’, rather than ‘grid to top of the tail resistor’.

[tubeswell]

300-310V is a typical plate idle for EL84s in many guitar amps. Even 350V is not unusual. Russian (Soviet era) ’EL84M’ can handle voltages a wee bit higher still and run reliably. Depends somewhat on design detail and tube manufacturing quality, but the main limiting factor to higher voltages is arcing across the closer spacing between electrodes in the miniature envelope (compared to octal tetrodes and pentodes).

[Lectroid]

@tubeswell,
Thanks for the longer explanation.   Knowing more about the "why"always helps.

@pdf64,
I'm new enough to this that I can't really evaluate your critique one way or the other.  It's a Hoffman design.  Maybe he's addressed this issue before?

[jordan86]

I like a 5V rectifier purely for the sake of “options”. 5V rectifiers seem easier to source and experiment with. Although, I’m also (barely) a millennial so I have a hardwired fear of missing out and having better options. 

Ive played a trinity 18w amp that a friend built with an ez81. Sounded great. I don’t think it’s a tone decision, per se. Although everything does matter. I still prefer 5V for practical reasons.

Edit: 5V/octal socket route also give you the option for a plugin SS rectifier cap.

[sluckey]

It's a Hoffman design.  Maybe he's addressed this issue before?

It has been discussed. Doug says it works, so no need to change anything. To please pdf64 simply swing the jumper (on the bottom of the .022 cap) to the right. This connects the cap to ground. Or, you can look at the other Stout and wire it with NFB.

[Lectroid]

Everybody,

Thanks for all the good advice.  As usual, this is where I can get the best information.  I'm going to order up the  18W chassis and dive into it.

Look forward to more noob questions from me as I get deeper into it.