Transformers/suggestions for a possible 6K6 PP build?

[norstroms]

Hi all,

I wonder if this would be a bad idea. The project I am currently working on is pretty straightforward: I have a mid-70's Twin Reverb I've gutted and was planning on converting to a Deluxe Reverb-ish end result. 2x12 (WGS et65/vet 60 combo, 16ohm each for an 8ohm load), mid pots, normal channel is more or less "stock" tremolo channel has some tone variations, cathode/fixed bias switch, safety/performance mods, etc.

It occurred to me that 22-ish watt output may actually still be a bit much for me, living in an apartment and all. I've run across some threads with people discussing using 6K6 tubes in SE format, and I've seen some threads from people switching out the 6V6's in some circuits for 6K6's... The DR circuit as it is would destroy the 6K6's with the plate voltages being so high, so I'd either use one of the voltage-lowering tools I've seen discussed (like maybe the Weber V-Dump B+ Dropper or a VVR?) or else I'd just start out with more appropriate transformers.

I've looked at a Hammond PT that seems appropriate (P-T370FX - 275-0-50-275 150ma, 6.3V 5a, 5V 3a), and another Hammond OT that also seems appropriate (P-T125H - 10000 CT, 2/4/8 taps; or possibly the P-T1609 looks more beefy - 10000 CT, 4/8/16 taps).

The 6K6 is listed with a 12000 ohm plate-to-plate load resistance, typically wants to see ~285v on the plates...

I'm thinking the 6K6's would be a little bit quieter for the apartment setting, would break up sooner if I turned it up, the lower voltage from the PT would give me a browner sound overall?

Any thoughts on the idea of building the AB763 Deluxe Reverb circuit designed with 6K6's in mind? Am I on the right track or does this seem like maybe not such a great idea? 

[tubenit]

My Tweed Overdrive Special has a 275-0-275  PT.  I used a 5Y3GT rectifier and 6K6 tubes and recorded this:

http://www.soundclick.com/player/single_player.cfm?songid=11527276&q=hi&newref=1

The Tweed BluezMeister should be able to produce a similar tone, IMO & it's a simpler build.

Both of these have layouts for them in the SCH files.  Nice thing about these amps is that you can pop in 5881's and a 5V4 or GZ34 and have around 23 watts .......... or use 6V6's for 14 watts.

With respect, Tubenit

[norstroms]

My Tweed Overdrive Special has a 275-0-275  PT.  I used a 5Y3GT rectifier and 6K6 tubes and recorded this:

http://www.soundclick.com/player/single_player.cfm?songid=11527276&q=hi&newref=1

The Tweed BluezMeister should be able to produce a similar tone, IMO & it's a simpler build.

Both of these have layouts for them in the SCH files.  Nice thing about these amps is that you can pop in 5881's and a 5V4 or GZ34 and have around 23 watts .......... or use 6V6's for 14 watts.

With respect, Tubenit

Alright! Thanks for all that, good to know. I've just recently started delving into the JSchem/.sch files. I like the idea of being able to swap around for different sounds. When you do swap in different tubes, wouldn't you need to change the cathode resistor, or does the 360R handle them all pretty well?

But in thinking of the output transformer, how important is matching the load resistance to the CT count? If the tubes want to see a load resistance of 12000, would it be advisable to get an OT with 10000 CT or can I consider OT's with 8000 CT? Is it better to get as close to 12000 as I can, or am I mistaken about these measurements being important in relation with each other?

I guess I also had a question about the 6K6's - it looks like they are not the easiest tube to find in matched pairs. Do people usually just buy a small lot of them and test in the circuit to find relative matches? I assume that must be the only good method at this time unless one of the current manufacturers comes out with a run of them.

[norstroms]

also re: choosing the right OT - with swapping in different tubes with their different outputs as you mention, I'm getting confused about whether I should be looking for an OT that goes up to the outputs you describe.

If the 6K6 puts out about 10 watts in push-pull, but the 5881 would put out about 26 watts if swapped into that circuit, would I look for an OT that is rated at 15 watts so that it's over-designed for the 6K6 but under-designed so to speak for the 5881's? (for instance, the OT intended to be "equivalent to 022913, 125A10B - 8 ohms. Princeton Reverb, Tweed Deluxe.") Seems like if I were to go down that road as you describe I wouldn't get the 26 watts out of an OT that's rated at 15 watts, it'd have to be an OT rated much higher and if I were using lower-rated tubes the OT would simply be over-designed for those tubes.

Like I said, I'm getting myself mired up in the details and losing site of the basics.  O_o

Thanks to any and all who feel like putting in .02

[tubenit]

I think the 5881's are kicking about 23 watts based on quasi output test across the speaker terminals.  I am using a 20 watt OT, but you could use a 25w OT if you wanted and it might give a tad more bass (which I don't think it needs).

I compared a 25w OT with a stock Marshall 50w OT and there was not much difference in size at all.

I am thinking the 6K6's are pushing about 8-10 watts max & closer to the 8 watts.

I never rebias anything. I simply swap tubes and I've had zero problems doing so.

With respect, Tubenit