6550 power tubes in an Ampeg V-4B?

[agedhorse]

I show the heater current for the PT is rated at 6 amps, the 6550 heater current is 1.6A each so the output tubes alone exceed the PT's safe heater current.

That said, there are other elements that are also limiting in the circuit which impact the performance.

Why not simply replace the tubes with 7027A's and be done with it? That's what the circuit is optimized for already.

 

[6thplanet]

Because people like to "upgrade"

 

[Sunnampeg]

See page 3, performance package. The package consisted of the four 6550 power tubes and a set of bear claws that fit the tubes. A re-bias was required. They claimed 135W output power.

For V4B amps with a vintage power supply, they may or may not stand up to the current draw of the 6550 heaters. It depends on the health of the transformer. A replacement PT should be fine if it meets or exceeds the original specs.

The 7027A tubes will safely draw the current that they need. The amp was designed to accept 6550 tubes. The amp runs 540V on the power tube plates. This is above the 450V maximum rating of a 6L6GC. So it will stress a 6L6GC.

https://www.talkbass.com/attachments/ampeg-brochure-v4-pdf.741460/

Thanks for the info . when you talk to adding the scree resistors how mush power will suck out of the output?

 

[Sunnampeg]

I show the heater current for the PT is rated at 6 amps, the 6550 heater current is 1.6A each so the output tubes alone exceed the PT's safe heater current.

That said, there are other elements that are also limiting in the circuit which impact the performance.

Why not simply replace the tubes with 7027A's and be done with it? That's what the circuit is optimized for already.

Yes, I've thought about it, honestly, but I do not know how the amp will sound with 7027A Tungsol— I've only had the old 7027, not the A, more or less headroom? Yeah, I probably will,

 

[beans-on-toast]

Thanks for the info . when you talk to adding the scree resistors how mush power will suck out of the output?

1K is doubling the screen resistor value. The screen current is reduced. It amounts to a low number of watts. Most of the power comes from the plate to cathode.

 

[Sunnampeg]

So in the end, i ve tried the amp with different cabinets and on the 2x12 i can hear more grind on the 810 and the 215, less drive, also readjusted the bias and place the sovtek 12ax7A as v1 which is a low gain12ax7, so for the moment I'm sticking with the 6550 tried it sounds slightly cleaner than before, or to say it better, the drive is smoother and it blends better with the sound, so it's less noticeable, also a bit more low-end.