All the 6550 talk, question for Peter

cml694 · **Posted:** Fri, May 28, 2010 6:03pm

So with all the talk about the 6550s in the VH4, I may give them a try in my Herbert soon. Just want to make sure that I can safely run them or does Peter recommend against using them?

Thanks!

Mizati20 · **Joined:** Mon, Dec 14, 2009 11:31pm **Posts:** 390

He flat out told me in my other thread that he does not recommend them for several reasons... but I ordered some anyway

cml694 · **Posted:** Fri, May 28, 2010 7:18pm

Mizati20 wrote:

He flat out told me in my other thread that he does not recommend them for several reasons... but I ordered some anyway

Well I wasn't sure if that was just directed towards the VH4/

racerevlon · **Posted:** Fri, May 28, 2010 7:34pm

I asked about this in another thread as well--does Peter not recommend the 6550's in the VH4 due to sound issues or due to the poor reliability of the 6550's he was receiving? It seems the VH4 came stock with 6550's for a long time and Diezel stopped using them because of breakage, not poor tone. Can anyone please clarify? I'm on the verge of buying a set of 6550's to use in my VH4, but if there's some other reason I shouldn't, I'd like to hear it sooner than later.

Cheers,

Race

bronz79 · **Posted:** Fri, May 28, 2010 10:07pm

Here are some Peter's answers to your question.

viewtopic.php?f=14&t=55449&hilit=6550+lead

viewtopic.php?f=14&t=70495

He only suggest to not using 6550,KT88 for an important and logical manufacturer's reason:
-is better to have an amp always reliable than one with a (maybe) X% more tone goodies but a bit less reliable.

Peter Diezel · **Joined:** Sun, Jul 02, 2006 5:43am **Posts:** 2275

Thanks Bronz :thumbsup:

racerevlon · **Posted:** Tue, Jul 27, 2010 10:04pm

So, my VH4 now has a brand new matched quad of Ruby 6550's biased at 78 mA per pair. Sounds great. Not as compressed or low-end-ish as the EL34's. With the short amount of play time I've put in I dare say I like it much better, but time will tell.

Question--what's the other trim pot on the opposite side of the board for? I don't see any references to it in the bias instructions, so I left it alone, but really want to know what it does.

Thanks! Clips soon!

Ventura · **Posted:** Tue, Jul 27, 2010 10:17pm

racerevlon wrote:

So, my VH4 now has a brand new matched quad of Ruby 6550's biased at 78 mA per pair. Sounds great. Not as compressed or low-end-ish as the EL34's. With the short amount of play time I've put in I dare say I like it much better, but time will tell.

Question--what's the other trim pot on the opposite side of the board for? I don't see any references to it in the bias instructions, so I left it alone, but really want to know what it does.

Thanks! Clips soon!

It's a hum trim pot. Controls hum...
V.

racerevlon · **Posted:** Tue, Jul 27, 2010 10:18pm

Ah--cool, so I can increase the hum? Excellent... :loco:

RJF · **Joined:** Sun, Oct 04, 2009 4:55pm **Posts:** 535

If one has kept even just somewhat up with the Diezel forum, it should be clear that Peter does not recommend 6550's due to lots premature tube failure, and he doesn't like the heat associated with the amp biased high enough to really get 6550's cooking hard.

What I have gathered, is that unofficially, he is saying that if you are going to run 6550's or KT88's, bias them at 60ma to reduce heat build up as much as possible, thus hopefully increasing reliability. I run my sextet of KT88's in my Herbert at 58ma and couldn't be happier.

Ventura · **Posted:** Tue, Jul 27, 2010 10:43pm

RJF wrote:

If one has kept even just somewhat up with the Diezel forum, it should be clear that Peter does not recommend 6550's due to lots premature tube failure, and he doesn't like the heat associated with the amp biased high enough to really get 6550's cooking hard.

What I have gathered, is that unofficially, he is saying that if you are going to run 6550's or KT88's, bias them at 60ma to reduce heat build up as much as possible, thus hopefully increasing reliability. I run my sextet of KT88's in my Herbert at 58ma and couldn't be happier.

Unofficially, that is correct - rather than get inundated with client/customer complaints and concerns with running 6550's, Peter said screw it. Back to EL34's. I love the tone of the 6550's and have them biased at 70mA per pair. Done. If they blow? I won't be bitching to Peter, I know they're passe in the world of Diezel reliability... But I love the 6550's - so that's my story.

V.

HerbieBoogie · **Posted:** Wed, Jul 28, 2010 4:48am

cml694 wrote:

So with all the talk about the 6550s in the VH4, I may give them a try in my Herbert soon. Just want to make sure that I can safely run them or does Peter recommend against using them?

Thanks!

taking out the el34s i see :gethim:

just kidding man :thumbsup:

make sure you keep herbie cool if your gonna run those 6550's

PaulyPanacea · **Posted:** Wed, Jul 28, 2010 7:55am

i cant seem to bring myself to come back to the EL34s. the 6550s just sound so awesome.

Ventura · **Posted:** Wed, Jul 28, 2010 10:12am

HerbieBoogie wrote:

cml694 wrote:

So with all the talk about the 6550s in the VH4, I may give them a try in my Herbert soon. Just want to make sure that I can safely run them or does Peter recommend against using them?

Thanks!

taking out the el34s i see :gethim:

just kidding man :thumbsup:

make sure you keep herbie cool if your gonna run those 6550's

Dude, ya gotta change that avatar (Herbie Boogies and his Godzilla Cookie Monster)

racerevlon · **Posted:** Wed, Jul 28, 2010 11:04am

RJF wrote:

If one has kept even just somewhat up with the Diezel forum, it should be clear that Peter does not recommend 6550's due to lots premature tube failure, and he doesn't like the heat associated with the amp biased high enough to really get 6550's cooking hard.

What I have gathered, is that unofficially, he is saying that if you are going to run 6550's or KT88's, bias them at 60ma to reduce heat build up as much as possible, thus hopefully increasing reliability. I run my sextet of KT88's in my Herbert at 58ma and couldn't be happier.

Ok, so the recommendation is that I drop down from 78 mA to around 60 mA then? (This is my first go at power tubes and biasing so all the help is appreciated).

Cheers,

HerbieBoogie · **Posted:** Wed, Jul 28, 2010 3:26pm

Ventura wrote:

HerbieBoogie wrote:

cml694 wrote:

So with all the talk about the 6550s in the VH4, I may give them a try in my Herbert soon. Just want to make sure that I can safely run them or does Peter recommend against using them?

Thanks!

taking out the el34s i see :gethim:

just kidding man :thumbsup:

make sure you keep herbie cool if your gonna run those 6550's

Dude, ya gotta change that avatar (Herbie Boogies and his Godzilla Cookie Monster)

hahaha soon, i like it too much. it's really rediculous!

RJF · **Joined:** Sun, Oct 04, 2009 4:55pm **Posts:** 535

racerevlon wrote:

RJF wrote:

If one has kept even just somewhat up with the Diezel forum, it should be clear that Peter does not recommend 6550's due to lots premature tube failure, and he doesn't like the heat associated with the amp biased high enough to really get 6550's cooking hard.

What I have gathered, is that unofficially, he is saying that if you are going to run 6550's or KT88's, bias them at 60ma to reduce heat build up as much as possible, thus hopefully increasing reliability. I run my sextet of KT88's in my Herbert at 58ma and couldn't be happier.

Ok, so the recommendation is that I drop down from 78 mA to around 60 mA then? (This is my first go at power tubes and biasing so all the help is appreciated).

Cheers,

yep, run your bias 60ma or less.

Ventura · **Posted:** Thu, Jul 29, 2010 11:01am

RJF wrote:

racerevlon wrote:

RJF wrote:

If one has kept even just somewhat up with the Diezel forum, it should be clear that Peter does not recommend 6550's due to lots premature tube failure, and he doesn't like the heat associated with the amp biased high enough to really get 6550's cooking hard.

What I have gathered, is that unofficially, he is saying that if you are going to run 6550's or KT88's, bias them at 60ma to reduce heat build up as much as possible, thus hopefully increasing reliability. I run my sextet of KT88's in my Herbert at 58ma and couldn't be happier.

Ok, so the recommendation is that I drop down from 78 mA to around 60 mA then? (This is my first go at power tubes and biasing so all the help is appreciated).

Cheers,

yep, run your bias 60ma or less.

Or, conversely, run it as you are until they pop and then load in a new set with a slightly lower bias...

V.

PaulyPanacea · **Posted:** Thu, Jul 29, 2010 1:52pm

Guess i had better turn my bias down..ALOT :yes:

racerevlon · **Posted:** Thu, Jul 29, 2010 1:58pm

Cool--thanks for the tips... does anyone ACTUALLY know what the other trim pot on the other side of the PCB does? I've received one hazing-style comment, but I'd really like to know what it does.

Cheers,

RJF · **Joined:** Sun, Oct 04, 2009 4:55pm **Posts:** 535

racerevlon wrote:

Cool--thanks for the tips... does anyone ACTUALLY know what the other trim pot on the other side of the PCB does? I've received one hazing-style comment, but I'd really like to know what it does.

Cheers,

I believe it has to do with helping to control the noise of the amp.

MARK2C · **Joined:** Fri, Aug 29, 2008 3:26pm **Posts:** 610

Like V said it controls the hum. The heaters require a resistance above ground to work properly and quietly.
The hum trimmer is a 100 Ohm pot that allows you to get the circuit quiet by having the perfect amount
of resistance to prevent noise. Usually around 50 Ohm or half way is perfect but the pot allows you to use
your ears to make sure it's perfect.

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All the 6550 talk, question for Peter

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