How difficult is it to change (2) 6L6 output impedance - OT Tran Matching?

[Jecarroll7]

Having trouble finding correct 5k to 4 ohm 30 watt (A frame) OT for a National Glenwood 90 (twin with reverb and trem). I can have one built, or mine rebuilt but the cost is 3 to 6x a new transformer, so option of last resort. I've also found a chinese one, but rather not go there.

I've read that the optimum impediance for a 6L6 amp is ~5500 ohms. And there are stock transformers available if I step up to 5.5 or 6K, or step down to 4K.

How difficult is it to change the output impediance?

Sorry, I don't have a schematic so just general advise would be appreciated.

[Steve Conner]

The optimum load impedance for a pair of power tubes is a function of the B+ voltage, screen voltage and screen resistors. However, it's not at all critical. Just use the 5.5k tranny, it will work fine.

[Jecarroll7]

Thanks Steve. Good to know. I worked a deal with Heyboer today to build a one-off based on the specs of the original with the same form factor. They still had the specs from when they did a run for Valco back in the 60's. Its a little more but not crazy, and a 3-4 week lead time but it will bolt right in. They've been great to work with so far.