converting el34s to 6550 tubes

Joined: 13 Feb 2004 Posts: 5603 Location: phoenix az.

so what all does this entail been thinking of coverting on of my marshall heads.What is the process of this and what kind of modification would this mean?expense wise to?

Joined: 12 Oct 2004 Posts: 3840 Location: BOSTON

what a coincidence i just ordered 4 6550's from tubedepot for my Diezel.

the only tech part i know of is the need to have the amp biased, and i'm taking it to someone to do that because i don't know what i'm doing and i don't want to electrocute my balls off.

Joined: 28 Mar 2006 Posts: 5465 Location: White Haven,Pa

I have 6550's in my JCM 800 and all I had to get done was a rebias.

Joined: 27 Oct 2010 Posts: 721 Location: Greenwood, IN

al wrote:

...because i don't know what i'm doing and i don't want to electrocute my balls off.

Joined: 27 Feb 2006 Posts: 13396 Location: Earth

Some resistors have to be changed. There are a few things that need to be done to make it work properly. It’s more than just a re-bias. My JCM800 uses 6550s and I love it.

Joined: 28 Mar 2006 Posts: 5465 Location: White Haven,Pa

Lanning is Killdozer wrote:

Some resistors have to be changed. There are a few things that need to be done to make it work properly. It’s more than just a re-bias. My JCM800 uses 6550s and I love it.

My amp tech must have just did what he had to do when he retubed it with the 6550's without telling me all what he did to make it happen Laughing

All I know is it rips with the 6550's Laughing

Joined: 27 Feb 2006 Posts: 13396 Location: Earth

Eternal Scar wrote:

Lanning is Killdozer wrote:

Some resistors have to be changed. There are a few things that need to be done to make it work properly. It’s more than just a re-bias. My JCM800 uses 6550s and I love it.

My amp tech must have just did what he had to do when he retubed it with the 6550's without telling me all what he did to make it happen Laughing

All I know is it rips with the 6550's Laughing

There are a few resistor values that need to be changed. It’s not an expensive modification. I agree that 6550s are the way to go. They used to come with 6550s in the states because there wasn’t a good supply of EL34s at the time. That and 6550s are far more reliable.

Joined: 12 Oct 2004 Posts: 3840 Location: BOSTON

6550's are chuggin thunder

Posted: Wed Apr 25, 2012 9:38 pm

Lanning is Killdozer wrote:

Eternal Scar wrote:

Lanning is Killdozer wrote:

Some resistors have to be changed. There are a few things that need to be done to make it work properly. It’s more than just a re-bias. My JCM800 uses 6550s and I love it.

My amp tech must have just did what he had to do when he retubed it with the 6550's without telling me all what he did to make it happen Laughing

All I know is it rips with the 6550's Laughing

There are a few resistor values that need to be changed. It’s not an expensive modification. I agree that 6550s are the way to go. They used to come with 6550s in the states because there wasn’t a good supply of EL34s at the time. That and 6550s are far more reliable.

Yep, one of my SL-X's had 6550's. Never heard of having to change resistors (just a rebias) but you learn something new everyday

EDIT - I never looked at the internals so it probably is as you said. I know Marshalls got 5881's at one time also in the 900 series. I know the 5881 equipped amps ran a lot cooler

Joined: 27 Feb 2006 Posts: 13396 Location: Earth

Northwinds wrote:

Lanning is Killdozer wrote:

Eternal Scar wrote:

Lanning is Killdozer wrote:

Some resistors have to be changed. There are a few things that need to be done to make it work properly. It’s more than just a re-bias. My JCM800 uses 6550s and I love it.

My amp tech must have just did what he had to do when he retubed it with the 6550's without telling me all what he did to make it happen Laughing

All I know is it rips with the 6550's Laughing

There are a few resistor values that need to be changed. It’s not an expensive modification. I agree that 6550s are the way to go. They used to come with 6550s in the states because there wasn’t a good supply of EL34s at the time. That and 6550s are far more reliable.

Yep, one of my SL-X's had 6550's. I thought all Canadian 900 series amps came with them anyway. US got the EL-34's. Never heard of having to change resistors (just a rebias) but you learn something new everyday

It would be cool to be able to choose between the two with just a re-bias but that’s not the case. I’m sure they could mod the amp to be able to accept both tubes. I know the Slash amp has an auto-bias feature and can accept other types of tubes but that’s the only Marshall the I know of that can do it. The JCM800s that are biased for EL34s need a bias mod to be able to bias for 6550s and vice versa. The EL34 bias range resistor is 220K and the 6550 bias range resistor is 150K. It’s not a hard thing to do.

Joined: 23 Nov 2005 Posts: 8256 Location: Ontario, Canada

It's real easy to change a bias resistor. There is one for each bias pot. I changed one resistor when I modded my peavey to get it running hotter.

Joined: 07 Aug 2007 Posts: 2740 Location: Southeast MI

If I'm not mistaken I think you should change the screen resistors on the Marshalls too. I don't remember the value off the top of my head.

Joined: 29 Nov 2003 Posts: 12253 Location: PEORIA ILLINOIS

el34s are way nicer than 6550s.

Joined: 27 Feb 2006 Posts: 13396 Location: Earth

BLOODROOT wrote:

el34s are way nicer than 6550s.

Depends on the amp. I’m happy with my tone with the 6550s and I also like EL34s but the 6550s have higher headroom and more clean, low end power. That’s desired by some of us. EL34s also don’t last as long as 6550s.

Joined: 28 Mar 2006 Posts: 5465 Location: White Haven,Pa

Lanning is Killdozer wrote:

BLOODROOT wrote:

el34s are way nicer than 6550s.

Depends on the amp. I’m happy with my tone with the 6550s and I also like EL34s but the 6550s have higher headroom and more clean, low end power. That’s desired by some of us. EL34s also don’t last as long as 6550s.

+1

Joined: 28 Jul 2004 Posts: 956 Location: D.O.A. 04-00341

For 800's 100w range resistor from 27K to 15k, ( in bias supply section) ( this not the 47k course adjustment resistor " it does affect range but is a fine range)- ( grid leak ) These are between the PI and power tube from 220K to 150k for a 6550, dont worry about the NFB wire change .. leave it alone

Thats it..

EDITED TO AVOID CONFUSION

Joined: 12 Oct 2004 Posts: 3840 Location: BOSTON

i like EL43's, 6550's and KT88's

6L6's piss me off.

Posted: Thu Apr 26, 2012 7:29 am

Lanning is Killdozer wrote:

BLOODROOT wrote:

el34s are way nicer than 6550s.

Depends on the amp. I’m happy with my tone with the 6550s and I also like EL34s but the 6550s have higher headroom and more clean, low end power. That’s desired by some of us. EL34s also don’t last as long as 6550s.

Yep,

I have 6550s in my 50 Watt. EL34s in my 100. The hotter transformer on the 50 required 6550s. Much ballsier sound too. Sometimes I think my 50 is louder than my 100.

Posted: Thu Apr 26, 2012 7:30 am

al wrote:

6L6's piss me off.

That's because they only work good in Boogies.

Laughing

And JFTR.. A Rectumfryer is not a Boogie.

Joined: 28 Jul 2004 Posts: 956 Location: D.O.A. 04-00341

Lanning[/quote]Yep, one of my SL-X's had 6550's. I thought all Canadian 900 series amps came with them anyway. US got the EL-34's. Never heard of having to change resistors (just a rebias) but you learn something new everyday[/quote] It would be cool to be able to choose between the two with just a re-bias but that’s not the case. I’m sure they could mod the amp to be able to accept both tubes. I know the Slash amp has an auto-bias feature and can accept other types of tubes but that’s the only Marshall the I know of that can do it. The JCM800s that are biased for EL34s need a bias mod to be able to bias for 6550s and vice versa. The EL34 bias range resistor is 220K and the 6550 bias range resistor is 150K. It’s not a hard thing to do.[/quote]

This is referring to the grid leak , not range resistors they are two different things

I edited my instruction post to avoid confusion between resistor and section types

Joined: 29 Nov 2003 Posts: 12253 Location: PEORIA ILLINOIS

Lanning is Killdozer wrote:

BLOODROOT wrote:

el34s are way nicer than 6550s.

Depends on the amp. I’m happy with my tone with the 6550s and I also like EL34s but the 6550s have higher headroom and more clean, low end power. That’s desired by some of us. EL34s also don’t last as long as 6550s.

that is true and the player. and I just realized, its the 6550s I like and kt88s I despise. my savage came with 6550s which were badass and then I put kt88s in it because I read on an audiophile site they were better. I beg to differ. Thinking they should be virtually the same, they are not. the kt88s are huge, full and warm but have a wierd feel to them. they are very sterile feeling like playing emgs with passives. hard to explain. so yea 6550s are good. I still like el34s better but you are correct , 6550s have headroom for days