Can I use 5881 pair on Hammond 1760H?

[psychepool]

I made Plexi 6v6 with Hammond output transformer. (1760H)
http://www.hammondmfg.com/pdf/EDB1760H.pdf

I use JJ 6v6, and bias setting is about 20mA.
(The plate voltage is DC420v)

Can I replace 6v6 with 5881 for more output?

[Littlewyan]

I think you'll be pushing that transformer a bit too much with 5881s. You wont get a massive increase in output anyway, it'll be just about noticeable.

[martin manning]

Maximum power output is more a function of the plate voltage and load impedance. The tubes and the output transformer then have to be capable of handling that power. Your OT is rated at only 20W, so it is pretty much on the edge as it is.

If you just replace the 6V6 with 5881 you will hear some difference because the 5881's transconductance is higher (more current for a given drive signal). If you drop the load impedance by half to 3300 (run an 8 ohm load on the 16 ohm tap, say), you'll get a big power increase. However, 3300 is too low for 5881, your OT is spec'd at 20W, and your power supply might not be able to keep up.

I would say you need at least a 4k 40W OT, like for a Fender Vibrolux say: http://www.classictone.net/40-18006.html . You could then mismatch it the other way (8 ohm load on the 4 ohm tap) to get an 8k primary for 6V6's.

[Littlewyan]

What speaker cab are you using? Getting another speaker cab or upgrading from a 2x12 to a 4x12 will probably increase the volume more than replacing valves.

[John_P_WI]

Guys, not knowing the power transformer used - swapping to different tubes will not magically increase power out, there may only be the potential for "20 watts" available. Additionally, there are many amps out there that have around 1k7 impedance for a quad - therefore 3k3 is not too far off for a pair IF you play the speaker load mismatch game...

Just my diminishing 2 cents.

[psychepool]

Thanks all. It will be not effective choice because the limit of output transformer specs.
I'll just need to keep a 6v6 tubes. Thanks

[goldenGeek]

I have used Hammond 1750H (same as 1760H but with just the 8ohm tap) and 1760H with multiple 6L6/5888 and EL34 builds. But The power transformer has to be able to deliver enough current for it to work. One of my favourite builds is a 2061x with EL34. Almost identical circuit as the EL84 version but I used the Hammond replacement for vintage AC30 for power... 290NX if I recall. You wont get a much louder/powerful amp (because of the low plate voltage), but it's more than 20W so the trafo can take some serious beating... it sounds awesome (to me anyway).