which OT would you choose?

[phydauex]

Howdy All,
In the process of rebuilding a butchered Bandmaster head that had an assortment of iron from different amps. What I'm planning on doing is using a quad of 6V6's in it and I have the choice of either a JMP style 3.2k/50 watt OT or a SF Bassman 4k/50watt. I'm not concerned really about secondary taps, one has 4/8/16 the other 4 ohms. My head scratching has come from looking at tube data: pair of 6v6's at 14 watts into 8000 imp (albeit at 350 volts) or Fender Deluxes that run 6v6's into a 6.6k OT. Which is why I initially picked up a 3.2k OT. I'm going to use the Twin power transformer that was in the amp and probably use a choke input psu to drop the voltage hopefully down between 400v and 420v.

Which would you use and why?

Thanks for any and all suggestions.
ps If I don't use the 3.2k OT in this amp , I have a Plexi clone that would love to have it.

[ThermionicScott]

I'd pick the 3.2k -- it's as close as you can get to half of the DR's 6.6k. Forget what the tube manual says to do at 285V.

-Scott

[KevinOConnor]

Hi Guys

I wouldn't bother with the choke-input supply as there is no reason to drop the voltage for the 6V6s. You don't say which "Twin" PT you have: older ones produce about 470Vdc where the newer ones were at 500Vdc. Either voltage is fine for 6V6s provided you increase the screen resistors to correct values: 1k-5W per tube as a minimum, up to 2k2-5W. You should make this change even with 6L6s.

The application notes in tube data sheets are just that: applications. They do not usually represent the maximum capability of the tube. A pair of 6V6s easily produces 30W of clean sine-wave power in the correct environment. Four will produce more.

As illustrated in TUT, four 6V6s in a mid-80s Twin reverb produces 48W into both an 8R and 4R load using the stock Twin OT. This amp had 470Vdc, the same as the Deluxe at that time.

You can use either OT that you have. Tack solder one in and try it. See how much power you get and if you like the sound. Try the other one, then make a decision and fully mount and wire the selected unit. neither one will be completely wrong.

Have fun
Kevin O'Connor

[Wilder Amplification]

Howdy All,
In the process of rebuilding a butchered Bandmaster head that had an assortment of iron from different amps. What I'm planning on doing is using a quad of 6V6's in it and I have the choice of either a JMP style 3.2k/50 watt OT or a SF Bassman 4k/50watt. I'm not concerned really about secondary taps, one has 4/8/16 the other 4 ohms. My head scratching has come from looking at tube data: pair of 6v6's at 14 watts into 8000 imp (albeit at 350 volts) or Fender Deluxes that run 6v6's into a 6.6k OT. Which is why I initially picked up a 3.2k OT. I'm going to use the Twin power transformer that was in the amp and probably use a choke input psu to drop the voltage hopefully down between 400v and 420v.

Which would you use and why?

Thanks for any and all suggestions.
ps If I don't use the 3.2k OT in this amp , I have a Plexi clone that would love to have it.

14 watts is not the power output. That is the maximum average power that the plate itself is capable of dissipating (i.e. the average power the plate dissipates over the period of one cycle of the AC sine wave output). It tells you nothing about output power. What it DOES tell you though is the minimum safe load impedance at a given B+ you can run them on.

However, there is "minimum safe load impedance for the B+ voltage" and then there's "optimized maximum power transfer" load impedance, which you would need to draw a load line for.

A pair of 6V6s can run safely into a 7.2K plate-plate load at a B+ voltage of 450V. Half that for a quad of them.