Vintage SVT with 6L6GC?

[okcrum]

I run NOS GE 6550A's in my SVT. The line voltage in my area is 118VDC so I never get over 700V. What you have to keep in mind is that the data sheet specifications for a tube are intended to provide an optimal service life. Designers often exceed the specs. It doesn't necessarily mean that the tube will melt. It could mean that tube life will be shorter. How much shorter, if at all, depends on the tube design. Some tubes are rated conservatively, some aren't.

Older Traynor comes to mind when I read "Designers often exceed the specs."

At 125 VAC on the power, I've used new Tung Sol, Sovtek, and Electro-Harmonix (old) 6550 so for sure New Sensor brands will work.

 

[webmonster]

I run NOS GE 6550A's in my SVT. The line voltage in my area is 118VDC so I never get over 700V. What you have to keep in mind is that the data sheet specifications for a tube are intended to provide an optimal service life. Designers often exceed the specs. It doesn't necessarily mean that the tube will melt. It could mean that tube life will be shorter. How much shorter, if at all, depends on the tube design. Some tubes are rated conservatively, some aren't.

Good points.
OTOH several techs here in NZ were finding that a 'large' number of JJ KT88s were failing very quickly with more than c.550V (Holdens and Jansens run their 6550s or KT88s at 650+).

The 6550 heater draws 1.6A per tube. The 7027A draws 0.9A per tube. Your heater circuit would have to be capable of handling 0.7A of additional current per tube. If you amp has two tubes for example, that's an additional 1.4A that would be needed. Whether or not you amp can deliver this without taxing the power transformer depends on the design of your amp. If you had a model number for the power transformer you could look up the specs and see how much current the 6.3V winding can supply.

I looked at the Jansen Bassman 75 schematic and didn't see a transformer spec. They might be able to tell you at Jansen Link Removed. I take it that John Veldwijk is the technical guy to talk to. I would also ask them how they think the amp would perform with 6550 tubes installed. The designer knows what the output transformer specs are and what it is capable of. Knowing the impedance would help determine if the 6550's would be a good match for the output transformer.

John V is a good contact to have - I got his email address a couple of months ago. Not sure if he would have the data for transformers because they used several NZ manufacturers over the years. But I should ask him
Early versions of the Bassman 100 had 4x 6L6's, but I've seen a schematic for a silverface Bass 100 that used two 6550s (at 680V).

Jansen as a company doesn't really seem to acknowledge their vintage products; I would have thought it was good (and inexpensive) PR for them.