Metropoulos Forum

I'm currently building a '69-style SL, and I want to try it with 6550 tubes.

- does a Tung-Sol 6500 (original 50s-60s production) fit in a 69 SL? With the rotated output transformer and large envelope of the "coke bottles", I am a little worried that there's not enough clearance? Anyone tried this?

- do I *have* to change the 220k bias splitters to a lower value? Some say 150k, some say even lower. How do EL34s sound with a lower value resistor? Hiwatts have 100k, yet use EL34s... Looking for a BOG type sound.

Anyone?

Didn't Robin Trower use 6550's in his old Marshalls? Tuned his Strat down a whole step and used a pedal with it? Sounded GREAT...

Never heard about that, but I love his sound as well, so that works for me!

I have a 12-series already and am currently building a 69 SL. I'll probably set up one with EL34s and one with 6550s, just don't know which tubes in which one.

Should be plenty of room for them I would think. Yes you need to change the bias splitters to at least 150K, I run 82K in my 6550 amps but 150K works just fine and you will have to increase - bias in the bias circuit as well.

shakti wrote:I'm currently building a '69-style SL, and I want to try it with 6550 tubes.

- does a Tung-Sol 6500 (original 50s-60s production) fit in a 69 SL? With the rotated output transformer and large envelope of the "coke bottles", I am a little worried that there's not enough clearance? Anyone tried this?

- do I *have* to change the 220k bias splitters to a lower value? Some say 150k, some say even lower. How do EL34s sound with a lower value resistor? Hiwatts have 100k, yet use EL34s... Looking for a BOG type sound.

Hi
have no ideea how those 6550 sound, but changing values of resistors have less in common with the power tubes in terms of sound but more for proper functioning of power tubes.
In terms of sound those resistors have major impact for PI tube cause you will modify the load "seen" by PI tube. lowering will have as consequences less gain (due to less amplification)/early brek-up-less headroom (due to reduced voltage swing)and of course you will have less bass reponse cause the time constant will be modified if you keep the same caps in circuit. "less"doesn't have any depreciative conotation just to be very clear the sound will be changed once you change those resistors over the particularity of any power tube you decide to use.
And yes , you will need to lower in value.100k or less is relative safe for those tube,but can choose 150k as well for the tone -as Marshall used-for tone consideration. Hope this help
Catalin

Tung Sol RI 6550's worst tone 6550 ever. I had 4 quads. suck, thin, no lows compared to Sovtek or SED, even Svetlana. 2 of them ended up having vacuum leaks too and turned white in a matter of 2 gigs. My 2 cents.

Try the TAD 6550A I just put them in a JMP 2203 and they sound great