Transformer “voicing”?

[jordan86]

Thinking of building a 6L6 blackvibe. Single channel blackface, no trem, no Reverb. Venturing into uncharted waters. What I DONT want is a sterile, shrill, clean tone. Thinking that having a slightly under spec’d transformers would produce a more satisfying amount of compression and natural saturation. (Ala Vibrolux transformers, not Vibroverb transformers).

Is that thinking correct? Like would 35W transformers be sweeter, or just be a power limitation (possibly feel too saggy, loose). Thinking plate voltages on the 6L6’ more in the 430v range instead of 460v range.

What do you more experienced builders prefer?

[ac427v]

I think it's all about room size and audience.

Big room and loud audience equals high voltage and 6L6.
Small room and quiet audience equals low voltage and 6V6.

[Latole]

You mean output transformer.

The mod you are talking  ; Is that thinking correct ?

Short answer ; Not on my opinion. It could be a part( not sure ) of what you are looking.

"Low" power speaker may help too.

[tonepumpamps]

I've had experience with over spec'd OT that might be of help.
I had a customer bring me a tweed bandmaster (5E7) clone from one of the bigger boutique amp companies.  My customer is a big tweed amp fan and said it didn't sound like a tweed at all.  It had super tight bass response and a shrill top end.
I took the back cover off and it looked exactly like a stock 5E7 circuit.  The filter caps were 16uF and the rectifier was a 5u4GB.  From the look of the circuit it should have had all kinds of sag and a looser bass response.
My customer said in the specs of the amp it said it had a "slightly larger" OT for "deeper bass and high end extension".  I pulled the chassis and what I found was an OT that was as big or bigger than any 100W amp I've worked on.
I replaced that with a traditional 5E7 spec'd transformer and it was pure tweed tone.  No more harsh highs and a lot tweedier bass response.  I should also mention that the customer wanted a little tighter bass after replacing the OT so  I upped the filtering slightly to improve the bass response. 

Hope this helps.

[shooter]

my2c;
"Voicing" is such an individual thing that what happens for me has very little to do with you.

capturing "that sound" from 50yrs ago, today, is like Mr Cash's Cadillac 

The better hunt might be something like;
play 10 amps, pick the closest to your "hunt", steal the design, build, then tweak one piece at a time 

[brewdude]

I recently built an amp inspired by the blonde era Fenders.
Its not true to any vintage schematic. 


I have a pair of 5881's with ~370v on the plates using a Magnetic Components 40-18088 (40W/6k primary), which I believe is the Vibroluxe size OT.
I'm pretty happy with it... Honestly, its too loud for my modest needs, but sounds and "feels" good to me... I think I like it better than most of the amps I've built with relatively larger OT's.

[Tone Junkie]

I like both 6l6 and el34 tubes with 370 to 380  b+ just seems to sound better to my ears.

[Joncaster]

I'm in the tuning phase of my build, with a huge PSE OPT that does 20hz-20khz. There's plenty of information there, that's for sure, but it's coming together nicely with some tuning decisions. I do know that it's a bit too wide band when the PA is full tilt overdriven, so I've had to tweak for that.
We'll see when it's done, but I don't regret going this large.

[shooter]

full tilt overdriven

SE/PSE driven into full OD typically isn't happy, but slightly bent with a oversized OT... that makes the tone ring out til next Tuesday 

[Joncaster]

full tilt overdriven

SE/PSE driven into full OD typically isn't happy, but slightly bent with a oversized OT... that makes the tone ring out til next Tuesday 

Haha, indeed that last turn on the master volume brings the heat, so it's currently benefiting from a touch of CFB from the secondary (about 3.5dB I think).
Luckily, I didn't have any rattiness or rasp to begin with, just overabundance of harmonics. But then I do need a reason to wire up a tone control...so.

[jjasilli]

To quote PRR, plagiarize.  I agree that [OT voicing] / [B+ voltage] is real; but it's all been done before.  E.g., many of the fender blackface era 6L6 (or 6V6 ) amps have very similar circuits.  Differences are in B+ voltages, PT specs, OT specs, SS or tube rectification; choke or no choke.  Pick the amp with the sound you want, then copy the topology.


"6L6 blackvibe. Single channel blackface, no trem, no Reverb."   

[HotBluePlates]

Thinking of building a 6L6 blackvibe. Single channel blackface, no trem, no Reverb. ... What I DONT want is a sterile, shrill, clean tone. Thinking that having a slightly under spec’d transformers would produce a more satisfying amount of compression

... Thinking plate voltages on the 6L6’ more in the 430v range instead of 460v range. ...

I have a 1967 Super Reverb, which would be on the stouter end of the blackface scale.  I haven't measured all the parameters of the power transformer yet, but 6L6 plate voltage comes in right about 415vdc.  I am knocking my wall voltage down to 115vac in general, as I'd have 127vac otherwise.

I've got a 1964 Deluxe Reverb.  It has the 125P23B power transformer. With 120vac input and 6.3vac measured on the filament string, I got 394vdc at the 6V6 plates when drawing 24.9mA of plate current per output tube. This was while using a Mullard GZ34.  Of note, the d.c. resistance of the high voltage winding is 220.4Ω, compared to 112.5Ω for a modern replacement PT.  The additional winding resistance likely contributes to the lower B+ in my amp.  My high voltage winding was delivering 334-0-334vac to the GZ34 rectifier (on par with what the new part claims), a fairly close match to the schematic even though 6V6 plate voltage is lower than shown on the schematic.

• A different forum member measured voltages on his 1965 Deluxe Reverb.  It's not indicated on a schematic, but Fender changed the PT to model # 125P23C in his amp.  With 121.6vac applied, his transformer delivered 348-0-348vac to the rectifier, for 442vdc B+.  Turns out his transformer had a winding resistance of 122.3Ω, which factored into his higher voltage when drawing 20mA per output tube.
• When checking my 1965 Vibro Champ, the 125P1B (same transformer used in the blackface Champ, Princeton, and Princeton Reverb amps) needs a wall voltage of 106.9vac to put 6.3vac on the heaters (likely because it is underloaded).  In this situation, it delivers 323-0-323vac to the rectifier (higher than what the schematic says) and 366vdc to the 6V6 plate (also higher than what the schematic says).  My 6V6 probably didn't draw enough current, as cathode voltage was 18vdc rather than the 21vdc on the schematic.  However, the high voltage DCR is 378Ω, where a modern replacement has 277Ω.

Fender changed PTs and specs over time.  For example, the 6G3 Deluxe schematic says the PT is a 125P2A, but only the earliest ones got that transformer.  The later amps got a 125P17A and then a 125P23B (as I can tell you from owning a 1962 and a 1963 Deluxe).

I haven't measured every vintage amp I have, much less all the ones I used to own.  But your B+ output is a result of the a.c. voltage of the winding, filter cap value (more µF = higher voltage), PT winding resistance (more Ω = lower voltage), and circuit current draw.  My suspicion is modern transformer companies are winding their parts with lower resistance than at least some vintage parts, leading to higher B+ voltage and lower sag in use.  You get a brighter, punchier amp but is that what you wanted?

The "obvious fix" (short of buying a different PT, since few vendors provide DCR specs) would be to add some series resistance between the PT winding & rectifier plates.