I know its Probably been asked... 6550s in VM?

[Slashwannabe1]

Recently I picked up a set of Groove tube 6550s #5 value for a very rediculously cheap price from a going out of business sale. This place also used to sell Marshalls and said that 6550s would work in a VM if you were in a pinch and had blown tubes because they are in the KT66s family supposedly.

Obviously I wouldn't intend on running my Vintage Modern like this all the time and the smoothness of the KT66s are what I love and intend to keep, but will 4 6550s work in the 2466 Vintage Modern without mods or any adverse effects?

I'm looking at using them in the event of a power tube failure if I am able to use them.

[MKB]

They probably could be made to work, but you'd have to confirm they will work in the VM without rewiring the power tube sockets, and if you have the right bias voltage available. I doubt you could just plug them in and be safe, you probably would need to rebias. If for a given plate voltage you need a higher (in absolute terms) bias voltage with 6550's, you could have big problems if you just plug them in and not rebias.

You'd also have to confirm that the grid circuit design is compatible with 6550's; IIRC the grid resistors for 6550's had to be lowered quite a bit from the EL34 values in old Super Leads in order for them to work.

Also you'd need to confirm the screen resistors are compatible with 6550's. Other than those issues, you are probably OK. 6550's can handle the plate voltage, they are a real manly tube. What 6550's will do to the tone is another question entirely.

[DIDIER]

Recently I picked up a set of Groove tube 6550s #5 value for a very rediculously cheap price from a going out of business sale. This place also used to sell Marshalls and said that 6550s would work in a VM if you were in a pinch and had blown tubes because they are in the KT66s family supposedly.

Obviously I wouldn't intend on running my Vintage Modern like this all the time and the smoothness of the KT66s are what I love and intend to keep, but will 4 6550s work in the 2466 Vintage Modern without mods or any adverse effects?

I'm looking at using them in the event of a power tube failure if I am able to use them.

6550's are in the KT88's family, but 6L6's are in the KT66's family.
You'd need to rebias for sure, and make a grid resistor change.
Also, the transformers in the VM are not designed for such high current draw, you would probably be better off running only 2 6550's instead of the quarquet (same thing Steve mentioned about switching to KT88's).

[Slashwannabe1]

Good to know I'll probably sell the tubes to an AFD100 buyer for spares :)