NAD: Fortin Evil Pumpkin

[2dor]

@FourT6and2 how was your unit biased from the factory? I'm reading the manual & it says it should measure 72 mVDC at each one of the red bias points.

Mine's showing 32-33 mVDC:

Seems very cold / conservative compared to what the manual recommends. Just wanted to understand if yours was biased the same & if the 72 mVDC is the value I should go for. I've the stock tubes in the thing for now.

Thanks man.

 

[napalmdeath]

@FourT6and2 how was your unit biased from the factory? I'm reading the manual & it says it should measure 72 mVDC at each one of the red bias points.

Mine's showing 32-33 mVDC:

View attachment 444806

View attachment 444807

Seems very cold / conservative compared to what the manual recommends. Just wanted to understand if yours was biased the same & if the 72 mVDC is the value I should go for. I've the stock tubes in the thing for now.

Thanks man.

Somebody must've mucked with it. Is it used?

You should be measuring each side as a combined pair - 36mA each tube should read 72mA for the pair on both test points.

 

[2dor]

Somebody must've mucked with it. Is it used?

You should be measuring each side as a combined pair - 36mA each tube should read 72mA for the pair on both test points.

Nope - I bought it new. I'll bump it up to 72

 

[FourT6and2]

@FourT6and2 how was your unit biased from the factory? I'm reading the manual & it says it should measure 72 mVDC at each one of the red bias points.

Mine's showing 32-33 mVDC:

View attachment 444806

View attachment 444807

Seems very cold / conservative compared to what the manual recommends. Just wanted to understand if yours was biased the same & if the 72 mVDC is the value I should go for. I've the stock tubes in the thing for now.

Thanks man.

Yeah, go for 70mV - 72mV per test point. I'm also curious what tubes came in yours. The manual states one pair should be 6CA7 and one pair EL34. But mine came with four EL34, just two different brands. Not actual 6CA7.

 

[2dor]

Yeah, go for 70mV - 72mV per test point. I'm also curious what tubes came in yours. The manual states one pair should be 6CA7 and one pair EL34. But mine came with four EL34, just two different brands. Not actual 6CA7.

Thank you. Yeah, they're identical to the ones yours has - not the big 6CA7 I know of.

 

[napalmdeath]

Yeah, go for 70mV - 72mV per test point. I'm also curious what tubes came in yours. The manual states one pair should be 6CA7 and one pair EL34. But mine came with four EL34, just two different brands. Not actual 6CA7.

Probably Psvane.

 

[novosibir]

@FourT6and2 how was your unit biased from the factory? I'm reading the manual & it says it should measure 72 mVDC at each one of the red bias points.

Mine's showing 32-33 mVDC:

This looks like someone has biased the amp with 6L6's, then swapped in EL34's, but hasn't biased the amp again after the swap.

 

[2dor]

This looks like someone has biased the amp with 6L6's, then swapped in EL34's, but hasn't biased the amp again after the swap.

Could very well be - I don't know what the deal was but I've got it at 71 - 72 mVDC now and it sounds & feels better.

Appreciate all y'all replies folks - great crowd! Thank you!

 

[FourT6and2]

This looks like someone has biased the amp with 6L6's, then swapped in EL34's, but hasn't biased the amp again after the swap.

6L6 tubes do not physically seat all the way in this amp and Fortin also says not to use them. If this amp came new from the factory, I doubt it was biased with 6L6. But who knows.

The tube sockets are PCB mounted. But the socket itself is recessed below the surface of the chassis. So the base of the tube must physically fit through the hole in the chassis to fully seat. Most 6L6 tubes have bases that are too wide. Furthermore, the tube retainer bear claws' screws protrude higher than the surface of the sockets. So tubes with wider bases (6L6s) can't fully seat against the chassis either, causing the tubes to stick up even more. Silly design.

You can get tubes to fully seat by removing the bear claws.