Cheap little SE tube amp

[electrovice]

This looks like a nice simple project. I do have a few questions though.

Does this amp need a preamp to drive, or are you using a line level source that already has a volume control?

Doesn't a pentode amp typically have negative feedback?

What value of resistor would be appropriate if one were to strap the pentode as a triode? (I already have several nice non-ultalinear 5K transformer sets ).

I see that Edcor makes a transformer in their GXSE line ( GXSE5-8-5.5K) that has better bandwidth (40 hz rather than 70 hz) but less power capacity (only 5 watts). The price is the same. Do you think it would work ok?

Thanks in advance.
John

[scott17]

Hi John,

I use this amp connected to the line out of my PC, 2VRMS drives it just fine.

This amp is wired UL, but it could be wired pentode by just moving the 3.3K to the B+. I think that value is still OK. I personally try to avoid feedback if possible, but wired pentode it may be of benefit. The driver cathode bias section would have to be changed though for gNFB.

G2 has a 250V max according to the datasheet, for triode connection, possibly just use the same 3.3K? Maybe someone else could chime in here.

I think I would go for the 10W version, this tube wired pentode is over 5 watts output according to the datasheet. You would be surprised at how good the XSE sound though.

If you do build it, I would definitely change the 470uF 1st capacitor in the PS to 47uF or 100uF as suggested by EWBrown.

Scott

[scott17]

I use this amp connected to the line out of my PC, 2VRMS drives it just fine.

I looked back at my loadline documentation for this, actually 1V will drive this amp.