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.

(edited)

Some 6L6 tubes won't physically seat all the way in this amp. 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. Some 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 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.

 

[TexasBaritone]

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.

I’ve found that GE 6L6GC easily seat all the way against the chassis & the power tubes feel to me as if they are seated deep enough into the sockets. I’m thinking newer production 6L6 have wider bases? Jason Frankhouser is using 6L6GC in his personal Evil Pumpkin.

 

[John4021]

The original was 6550s and EL34s... I suspect Fortin did this so he could still say it was running "mixed tubes" without the additional production costs of using 6550s...

EDIT: it didn't embed the pic of the tubes so here it is

The old thread where Jason first got the Hulk-modded Fortin is over here

Thread 'Evil Pumpkin (aka Satan's Taint) pics...Fortin content'

Oct 8, 2009

My amp is ready...I won't get to hear it until I get home from tour right before Thanksgiving. Gives me something to look forward to though, that's for sure!!

...

• killertone
• Replies: 32
• Forum: Rig-Talk

Damn brother,
I remember that amp when it hit the forum here. ( years ago)
Was that yours?

 

[TexasBaritone]

Damn brother,
I remember that amp when it hit the forum here. ( years ago)
Was that yours?

It’s Jason Frankhouser’s signature Killertone amp. He loves 6550 & EL34 tubes, so it was his personal preference on his prototype. The production Evil Pumpkin is slightly different & has the addition of an incredible clean channel that rivals my Boogies. I know he has been running a pair of 6L6GC in his personal production amp, but can’t remember the exact tubes he’s using for the other pair.

 

[FourT6and2]

I’ve found that GE 6L6GC easily seat all the way against the chassis & the power tubes feel to me as if they are seated deep enough into the sockets. I’m thinking newer production 6L6 have wider bases? Jason Frankhouser is using 6L6GC in his personal Evil Pumpkin.View attachment 444881

That 6L6 all the way on the left in this photo... it isn't sitting on top of the screws for the bear claw? In mine, I couldn't get actual 6CA7 to fit, nor wold 6L6. This also means 6550 won't fit. The bases hit the screws. Removing the bear claws solves the problem, ignoring the gap between tube socket and chassis. The specific tube socket design used in this amp is meant to protrude through a chassis hole, not sit inside/below it. But whatever.

 

[TexasBaritone]

That 6L6 all the way on the left in this photo... it isn't sitting on top of the screws for the bear claw? In mine, I couldn't get actual 6CA7 to fit, nor wold 6L6. The bases hit the screws. Removing the bear claws was easy, but it struck me as an odd manufacturing oversight considering there's still a large gap between the tube and socket (which sits below the chassis).

It pushes against the side of the screws, but it isn’t on top. I do now see that the socket sits slightly below the chassis; however, it still feels like the pins push in relatively far and seat quite nicely.

 

[FourT6and2]

It pushes against the side of the screws, but it isn’t on top. I do now see that the socket sits slightly below the chassis; however, it still feels like the pins push in relatively far and seat quite nicely.

Yeah, some tubes have wider bases that cause them to sit on top of the screws. This means the tube can rock back and forth like a see-saw. The gap between socket and chassis is less concerning. But it's still a bit of an oversight. Like they could have simply used sockets that mount slightly higher, which would've solved both problems. The exact same socket brand offers them in different mounting heights for the same price.

 

[TexasBaritone]

Yeah, some tubes have wider bases that cause them to sit on top of the screws. This means the tube can rock back and forth like a see-saw. The gap between socket and chassis is less concerning. But it's still a bit of an oversight. Like they could have simply used sockets that mount slightly higher, which would've solved both problems. The exact same socket brand offers them in different mounting heights for the same price.

I’m guessing that’s likely why Fortin recommended against 6L6? Pins losing contact from rocking back and forth sounds like it could be a really bad issue.

 

[FourT6and2]

I’m guessing that’s likely why Fortin recommended against 6L6? Pins losing contact from rocking back and forth sounds like it could be a really bad issue.

I was wrong about that. I looked back at my email with them and they said best to stick with EL34 but 6L6 are also ok. I would remove the bear claws though.

 

[TexasBaritone]

I was wrong about that. I looked back at my email with them and they said best to stick with EL34 but 6L6 are also ok. I would remove the bear claws though.

I’m going to follow your advice and remove the bear claws.
I do have some spring loaded tube holders that can be mounted wider. I previously bought them for KT88s and then ended up not using.

 

[Techdeth]

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.

Odd

 

[technomancer]

It’s Jason Frankhouser’s signature Killertone amp. He loves 6550 & EL34 tubes, so it was his personal preference on his prototype. The production Evil Pumpkin is slightly different & has the addition of an incredible clean channel that rivals my Boogies. I know he has been running a pair of 6L6GC in his personal production amp, but can’t remember the exact tubes he’s using for the other pair.

Yep that's Jaon's original Marshall mod. Actually I think it went through two or three mods before ending at the EP circuit, then he had it for a few years, then they did the prototype. I'm sure @killertone can cover it next time he is on if he has time.