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PostPosted: Wed, Jan 31, 2018 9:17am 
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Hack

Joined: Wed, Jan 31, 2018 8:21am
Posts: 3
Hi there! I'm new here and didn't know where else to look for help.
I own a Diezel VH4S (yes, stereo) since 2001, and it's still a great amp! It was delivered with 6L6 but I changed very soon to EL34 and had no problem for many years. Being curious, I recently tested those TAD Pen Tone Class A converters with EL84 tubes (I believe they're similar to those yellow jackets many people use), for what I always thought is that my amp has two separated power amps as A and B channel (maybe that was wrong, though...). Well I like that other sound too, and the opportunity to blend the EL34 and EL84 sounds with the stereo master is great!
Now the problem:
I recently wanted to play the EL84 in Power amp section A through all 4 speakers of my Diezel 4x12 cab. Remembering the golden rule "never play a tube amp without speakers!", I thought it would be alright if I took out the fuses (1+2) of the EL34 tubes in power amp section B. Seemed to work for the moment, I just wondered that the tube fault led on tube 2 was lit. When after that I wanted to use my stereo setup again, power amp section B was absolutely silent, and no bluish glow inside the EL34 anymore. Seems like taking out the fuses doesn't turn the VH4S into a 50W VH4 :doh: . Section A is still fine, no tube fault led is lit.

Does anybody have an idea what this might be, or if it is a severe damage? I'm a bit worried right now...
Thanks for any replies!


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PostPosted: Thu, Feb 01, 2018 6:13am 
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Why not connect the "silent" side to any other speaker cab and turn the Master to zero.
This way you hear only the other side without ruining the silent one.

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PostPosted: Thu, Feb 01, 2018 7:56am 
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Hack

Joined: Wed, Jan 31, 2018 8:21am
Posts: 3
Thanks for your reply, mate!
Yeah I had the same idea, but unfortunately I had no other speaker cab at hand. For the future, I'll do that or at least check the option of using a dummy resistor first. But now the damage is done and I'm trying to get an idea how bad it is, respectively how expensive it might get. Maybe only the EL34 are broken, or anything worse? As I think about it... I'll swap the power tubes in A and B tonight, which should show wether it's the power amp itself or just the tubes (with a cab connected, of course ;) ).

...and as I think further about it... Wouldn't two switches make sense for the possibility to switch either stereo channel completely on or off as needed? For example, one low power setting for practicing and one high power for the stage? That amp would be even more versatile than it is already! Hmmmm... :confused:


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PostPosted: Thu, Feb 01, 2018 11:58am 
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Joined: Sat, May 06, 2017 4:21pm
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Location: Texas
So you did put the fuses back in the EL34 section?

And if so, one of the LED fault lights are lit? If the LED is lit, that means the fuse is probably blown.

Also when you are plugging in different tubes, are you re-biasing?


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PostPosted: Thu, Feb 01, 2018 1:27pm 
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Hack

Joined: Wed, Jan 31, 2018 8:21am
Posts: 3
Yes, I put them back in. But you're right, that would be exactly like me if I had forgotten.
No, after plugging the fuses back in, none was lit. Led 2 was lit only while the fuses were out.
Usually yes, but not this time. The amp was formerly biased all for el34, and TAD claims those el84-converters are auto-biasing, so I just pulled them out at one side and put the converters in.
The master on the el34 side was completely down, if that matters.

Edit:
I just made the test and swapped the tubes. Still section B which is silent, that means the amp is broken, not the tubes. :cry:
Also, there is now a loud hum on channel 3, which is even louder in channel 4.

Edit 2:
Further I've noticed that certain blue glow can only be seen inside the tube on position three, in the working section A. So I swapped both "A"-tubes 3 and 4. Now still only tube 3 has that blue glow, but the hum on channels 3 and 4 is gone. :confused:

Has anybody got a clue what's up with the amp?


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