Vvr and bias switching

[Mike-p]

Hello all, this is my first post!

I'm planning an amp based around the normal channel of a 6g5. I want it to sound like segeborn YouTube of the cranked brownface pro! Ha ha. Anyway I have a laney lc50 donor amp and budget is minimal so I'm reusing the el34 tubes although I may change power tubes in the future.

I will add a fixed/ cathode bias switch and vvr. Was initially thinking I would only use the vvr in cathode bias mode covering PI and PA. However, I was then considering that after I've had my fun and lost my hearing with the el34, I'd likely want to reduce volume and power so was looking at 6k6 or 6v6 tubes. Normal b plus will be around 400v, to high for 6k6 but maybe I could knock 100v off with the vvr then rebias for the 6k6 in fixed mode. If you think this would work, should I scale the PA only or continue with PI and PA?

Also any suggestions for 12 or fifteen inch speakers appreciated,  I only have a vintage 30 in the laney. I'm in Europe so weber speakers are rare and plenty expensive! Was thinking legends or maybe fullback?

Thanks all.

[passaloutre]

I recall the 6K6 need ing a very different output transformer impedance than EL34 or 6V6…

[Mike-p]

Seems like that could be managed with a bit of monkey business with speakers and switching between the 4 and 8 ohm output taps?

[kagliostro]

I've an old Geloso PA amp with  a pair of EL34 Power Tubes, B+ is 315V and Output Power 35W

Don't remember the OT Primary Z

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A thing to be considered is that EL34 tubes have an  High gain input, other tubes, like 6V6 and others, don't

EL34 = 11mA/V
6V6= 4.1 mA/V
6K6 = 2 mA/V

So your premp output swing will result poor to drive a 6K6 tube

Franco

[Mike-p]

The pro is obviously designed for 6l6 how does the mu of a 6l6 compare? Sorry I have tried Google but not got a clear answer and I don't believe the ai... anyway, I can adjust the PI easy enough later on to provide more swing can't i?, I just want to decide on the vvr/ power supply section, pa or pi and PA.

[kagliostro]

6L6 = 6000 Micromhos = 6 mA/V (a bit more than half of an EL34)

http://www.r-type.org/pdfs/6l6.pdf

https://tdsl.duncanamps.com/sheets/807/807.pdf


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The more people prefer PI + PA but I think you must give a try to only PA and then PI + PA

Franco

[Mike-p]

Thanks people, sketched out from the diode rectifier. The 6g5 schematic shows 460v to the OT whereas I'm only expecting 400v from my repurposed transformer. Would you advise reducing the dropping resistors along the b plus line or just build as is. Also splitting the b plus removes the effect of the choke from the rest of the b plus string, I can't imagine this will make a great difference.