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PostPosted: Thu, Oct 26, 2017 9:05am 
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Hack

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Hey guys,

I just bought my 2014 Diezel VH4 from Reverb (looks like it's in great condition, seller claims it was barely played) and it's my first tube amp. I bought an apex match quad JJ KT77 from antique electronic supply. I am using the tube amp doctor biasmaster. I also have tube amp doctor 12AX7 PreAmp tubes.

I hooked up my bias master and tubes and such. First off, I'm running the switch on EL34. When I checked the current, Tubes 1 and 4 were running at a good current- 32 mA which I wanted to crank up to 35 mA for a good bias for my JJ KT77's. However, tubes 2 and 3 were running near 45 mA. I tried playing around with the knob that changes the bias (I forgot the exact term), and I was able to get tubes 1 and 4 to 35 mA, but means that 2 and 3 went up to 47 mA.

I did some trouble shooting- changing tubes, probes, etc, and it turned out that it was the tubes themselves that were running too hot. I was wondering what I should do at this point? Buy new tubes? If I were to buy new tubes, should I just get an apex matched pair to replace tubes 2 and 3, or should I get an entire new quad?


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PostPosted: Thu, Oct 26, 2017 10:07am 
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It's a 4000$ tube amp with potentially deadly voltage inside. Why not take it to a tech?

Quote:
I tried playing around with the knob that changes the bias


Really, dude, do Peter Diezel, yourself and your unborn children a favour and let it do a professional.

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PostPosted: Thu, Oct 26, 2017 11:23am 
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Hack

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Vin Diezel wrote:
It's a 4000$ tube amp with potentially deadly voltage inside. Why not take it to a tech?

Quote:
I tried playing around with the knob that changes the bias


Really, dude, do Peter Diezel, yourself and your unborn children a favour and let it do a professional.



Thanks for the concern. I watched videos online on biasing so i'm aware that I need to keep one hand in pocket, etc. Also, I made fine movements of the knob to adjust the bias.


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PostPosted: Thu, Oct 26, 2017 11:25am 
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I watched heart surgery on television and I do not try it on my granny. ;)

I say nothing against your adjusting the bias. But there seems to be something going wrong which is obviously beyond your abilities and it cannot be fixed by people on the internet. End of story for me.

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PostPosted: Thu, Oct 26, 2017 11:34am 
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Hack

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Vin Diezel wrote:
I watched heart surgery on television and I do not try it on my granny. ;)



I get where you're coming from man, I really do. I just would like some help in regards to my issue.


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PostPosted: Thu, Oct 26, 2017 12:20pm 
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Get a new quad. Shelve out those 50 bucks. If it does not help:
I've given you the only reasonable and responsible piece of advice you are in need of. Take it to a tech if you do not understand what is going on with these electrons and stuff. WTF is wrong with you internet people?

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PostPosted: Fri, Oct 27, 2017 9:41am 
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My D-Moll also has the dual trim pots. It's a bit of a balancing act to hit target bias. You may need to bring down 2 and 3 to a bit below what you want then raise 1 and 4 to target.


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PostPosted: Fri, Oct 27, 2017 9:54am 
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you need to contact antique electronic supply and RMA the tubes, you got a poorly matched quad.

I've had this happen before with 1 tube out of a matched quad, tubedepot just send out a new tube to replace the one, and a return label for the mismatched one.
Now that's service :)


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PostPosted: Fri, Oct 27, 2017 12:17pm 
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Crunchtime wrote:
My D-Moll also has the dual trim pots. It's a bit of a balancing act to hit target bias. You may need to bring down 2 and 3 to a bit below what you want then raise 1 and 4 to target.



Vh4 Only has the one bias pot.

To OP: Get another quad if it does the same thing then there is another issue that needs to be looked at by a tech.


Last edited by Hey_bert_whtcha_doin_bert on Tue, Oct 31, 2017 2:32am, edited 1 time in total.

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PostPosted: Sat, Oct 28, 2017 12:15am 
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Sounds like they gave you two matched pairs instead of a matched quad. Rule of thumb is 10% difference. If you have the time to wait, you should call them and send them back for a proper matched quad.


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PostPosted: Tue, Oct 31, 2017 8:59am 
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CrazyNutz wrote:
you need to contact antique electronic supply and RMA the tubes, you got a poorly matched quad.

I've had this happen before with 1 tube out of a matched quad, tubedepot just send out a new tube to replace the one, and a return label for the mismatched one.
Now that's service :)

+1. Looks like the tube vendor sent a mismatched quad.


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PostPosted: Tue, Oct 31, 2017 11:03am 
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Hack

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So I got a new quad. So far I was able to get 3.5mA across all channels except channel 2- it's running at 3.7 it's just a little off.

Any advice? Keep it at 2, or move it to another channel?


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PostPosted: Tue, Oct 31, 2017 11:14am 
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What do you mean by "channel"?
I guess you mean they run at 35mA, not 3.5.
If one tube is 2mA off, it's a non-problem. :rock:

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Diezel 412 FL V30
Diezel 212 FL V30
ESP Horizon NT II
ESP Horizon NT II
USACG Strat Kinmans


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PostPosted: Tue, Oct 31, 2017 11:15am 
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Hack

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Vin Diezel wrote:
What do you mean by "channel"?
I guess you mean they run at 35mA, not 3.5.
If one tube is 2mA off, it's a non-problem. :rock:



woops, I meant 35 mA lol

For Channel, I mean "tube 2".


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