Output Xformer for both 6V6 and 6L6

[Nathan]

Hey all,

Say I was trying to build a circuit that could accommodate 6V6 or 6L6 easily.

And let's say the PT is a Hammond 270EX which can supply 275-O-275 and 4A on the 6.3V heaters (5 preamp tubes + 2 power tubes).

What parameters do I need to consider when choosing a suitable OT?

Thanks very much!

 

[Lowerleftcoast]

You would want a OT capable of handling the 6L6 tubes that has 4 and 8 (or 4, 8, 16) Ohm taps. Plug 8 Ohm speaker load into the 4 Ohm tap when using 6V6 tubes.

 

[2L man]

If you use power transformer which has dual HV outputs for example 325-275-0-275-325 it easy to get switchable two different high voltages installing a DPDT switch between secondary and rectifier.

Output transformer impedance is easy to manipulate for different tubes connecting loudspeaker to other output. Select OT for 6L6 tubes because it produce more power and work with lower power 6V6. Same effect comes when you use second parallel connect speaker when you use 6L6.

 

[bebopbrain]

6.6K ohm output transformer works nicely for both.

 

[Snfoilhat]

The three answers above may be all you need, but can we have more info about what you'd like to accomplish? Is the goal one amp that transforms from sounding like the power amp of (say) a Bassman to sounding like (say) a Deluxe, with the differences in power, etc? Or is one amp that preserves its own sound, whatever that ends up being, whatever compatible power tube the user slots in? Or something in between? What about user convenience (how easy is easy) -- how many switches or jacks/plugs is it ok to have to switch in addition to swapping the tubes?

 

[tubeToaster]

I built an amp that uses 2x 6V6 or 4x 6V6 or 2x 6L6. I used a Weber W404248 output transformer.
With 2x 6V6 I have 8 ohm and 16 ohm taps at 8000 ohm primary.
with 2x 6L6 or 4x 6V6 I have 4 ohm and 8 ohm taps at 4000 ohm primary.

W404248 Transformer – Weber Speakers

www.tedweber.com

 

[Nathan]

The three answers above may be all you need, but can we have more info about what you'd like to accomplish? Is the goal one amp that transforms from sounding like the power amp of (say) a Bassman to sounding like (say) a Deluxe, with the differences in power, etc? Or is one amp that preserves its own sound, whatever that ends up being, whatever compatible power tube the user slots in? Or something in between? What about user convenience (how easy is easy) -- how many switches or jacks/plugs is it ok to have to switch in addition to swapping the tubes?

Sure I'm going for a Mesa Blue Angel build but limited to the 6V6 side and (most likely) removing the effects loop and mojo module. I've owned 2 of these combos and like the sound a lot but often wonder how 6L6's would sound for a bit more headroom. To me it brings a DR sound but more guts. The stock OT is huge, about the same size as the PT but I gather it's partly to handle the EL84's when combined (I NEVER use them). I will only use one type at a time and I'm fully aware of the change in speaker load required.

 

[Nathan]

FWIW I actually have a Hammond 1760H here at home in a Blues JR. Will it be sufficient or limit the 6L6 option?

Basically I'd like to know how similar would it sound to the stock Mesa OT which must be designed for about 40 W but intended to handle both power tubes combined (2x6V6 + 4xEL84).

In other words, do I need to get a larger OT than what I would normally use for 2x6V6?

 

[printer2]

The transformer is rated for 20W. Do you want a 20W amp?

 

[2L man]

FWIW I actually have a Hammond 1760H here at home in a Blues JR. Will it be sufficient or limit the 6L6 option?

Basically I'd like to know how similar would it sound to the stock Mesa OT which must be designed for about 40 W but intended to handle both power tubes combined (2x6V6 + 4xEL84).

In other words, do I need to get a larger OT than what I would normally use for 2x6V6?

It depends of the B+1 and B+2 which together with OT impedance define the power output when tubes are capable to draw the current OT impedance can provide.

If you play constant full power power chords too small OT overheats and eventually destroy. It you play "dynamic music" where loud notes are rare it possibly won't burn and can bring interesting distortion to sound when OT only briefly saturate. 5E3 OT is quote small and it saturate when dimed. 5E3 phase inverter distort and then power tube drive signals come different and it must have significant effect to OT saguration.

Quite simple way to limit the max current power tubes can pull is lower Screen voltage and possiblyn also increase screen resistors value. Just a SPST switch and another resistor for B+2 drop Screen voltage when switch contact is opened. Or lower B+1 where there are many ways to do it but then there comes a question why use 6L6?

5E3 OT Hammond 1760E which is 15W rated weights 465g and H1750H 20W rated 658g so it is way too small for typical 6L6GC use which has potential for about three times more power.

 

[Nathan]

Alright I finally ordered a Hammond 1760JB for 40W with 6k primary.
This way I know I'll be safe with the 6L6's and it makes sense that the stock Mesa OT had to handle both power tube types in combination for 38 Watts. I feel pretty confident this is as close as I can get. If I really want to, I can pretty easily revert to the 20W transformer down the road. Thanks for all your input guys!