VH4 Tube-Channel Mapping (OK, now I feel like crying)

E

eonblue

New member
Alright, here is my quandry. I need my amp tommorow. I just got in my new set of tubes, but one was broken in shipping so I have to ship it back. So, I hooked up my Bias Rite yesterday to my old tubes and they were sitting around 30 for the bias reading. I plugged in my 3 new tubes + 1 old tube and checked the bias again. The new tubes read around 46 while the old was still at 30. So, I adjusted the bias to 35 for the new tubes. This caused the 1 old tube to read around 20.

Here is the question.

I only need to use channel 3. Is it possible to put the old tube in a non channel 3 slot without risking damage to the amp?

I only need to use it in this manner 1 time for about 3-4 hours.

Thanks a ton.
 
Powertubes are working for all channels.

Play the gig with a pair of your new tubes, set bias to 33mA with the Bias Rite and hook your cab (say its a 16 Ohm cab) to the speaker output of half of its mpedance ( 8 Ohm if its a 16 Ohm cab).
If its a 8 Ohm cab, use the 4 Ohm speaker out.

If you don't like the sound (smoother, just a bit) of the "half tube" version, run all of them with the new tubes based to 33mA.

Olaf
 
So, just to be clear, you are saying plug in only two of the four tubes and run my 16 ohm cabinet from the 8 ohm output on the head.

Should I put the two tubes in any particular slots (1-4)?

And btw, thanks.....


P.S. Do I need to watch out for cranking the master volume too loud or anything?
 
Sure. Put them either into the inner or outer sockets.

So either into 2+3 or 1+4 - sockets from the left: 1,2,3,4.
 
Ehh, not really that loud to be honest. Id say the loudest Ill need is 10-11 on the master with the channel volume at noon. If that..
 
Well thats medium I'd say.

To be full on the safe side, bias them to 30mA with your bias rite (don't get confused with the recommendations - you are reading the cathode current, while the recommendations are for the plate current).

And bring your old tubes to the gig.

Don't worry. Enjoy the gig with your amp !
 
So when my new tube comes in and I have a full set of four, what would you recommend for the bias setting using the Bias Rite?
 
You mean a completely new quartet?
31-33mA with the bias rite for EL34s.
Thats around 60% of their max. dissipation and IMO sounds good.

But in the end - yours ears decide. I wouldn't bias them hotter than 34mA, which would be 65%.
 
Alright, so I did as you described. I put the new tubes in positions 1 and 4. I biased to 30 as was prescribed to be on the safe side. So I turned it on, just cracked open in volume(less than 9 o'clock) and everything was great for about 5 minutes. Sounded great, extremely quiet when palm muted. Simply the Diezel sounding like it should. Well, then I got a a small pop, but everything acted fine, so I played for another minute.

Well, let me tell you that the next pop was NOT small at all. It was in fact a BANG. So, the result is that it blew both tube fault fuses and it completely DISENTEGRATED the mains fuse. I must say that Im not surprised. This initial problem started about a month and a half ago when the mains fuse blew along with the channel 3 tube fault. So I chalked it up to a bad power tube and ordered a matched quartet.

Well, it happened again and it happened really bad.

I want to jump off my balcony. I was so jacked about having my sweetheart back, but she brought me up....only to powerbomb me off the top ropes.

I need help.
 
You should definitely change your tube dealer. Sparks from the tubes cause the fuse to blow . . . - and thats what the fuses are inside the amp: to protect it from sparks thru faulty tubes.

I'm really sorry for you, but with average tubes this procedure (running with pairs only) isn't a problem at all. Get new fuses and tubes. Additionally your hum trimmer needs to be checked by a tech too . . . .
 
I really dont think its a problem with the tubes. I dont think its a problem with the procedure either. This happened with the last set of tubes as well, which were from the factory. Happened about a month ago. Blew one tube fault and the mains fuse with a pop.

The tubes came from an extremely reputable tube dealer on this site whose name I won't divulge because he is highly regarded here.

Is there anything that you can think of that might be wrong with the amp? I just want to get this problem fixed.

Btw, from appearance, it doesnt really look like the tubes are blown. But I'm assuming that I wouldn't be able to tell from looks alone?
 
Sorry, you obviously know more about these amps than me. Im just upset.

Ok, I still have two good tubes from the factory and fuses as well. I could try this again with those tubes.
 
Well, if the fuses blow incl. the mains it is caused by the tubes or the hum trimmer.

But I will give Peter a call and tell him to have a look here.
 
Thank you. Do you think it would be a worthwhile test to try this procedure with two of the old tubes which are still good?
 
Ok, so I put the new tubes in cause I was so antsy. I biased them to 30(sorry, I jumped the gun). So again, it plays fine for about 5 minutes(same as last night) and then...

There is a crackling sound and the amp cuts out completely. At that point I cut the power and let the amp rest for about 10 minutes to try and let any electricity dissipate.

So I plug it up again, and again....I play for about 5 minutes. This time....

There is a crackling sound followed by a really wierd low electrical humming.

Does that tell you anything?

P.S. I forgot to mention that I played at a VERY low volume and that in neither instance did any fuses blow.
 
Sometimes it´s a really mess with used or new tubes.
Maybe there is need for an experiencend tech.

1. Replace the power tubes with a quartet You know that really works.
2. Bias each tube to 35 milliamps.
3. Check the amp with master volume down.

If the noise disappers, the power tubes and the phase inverter
works well.

Turn the master volume up.

If You hear the noise again, replace the preamp tubes with a set
You know that´s ok. Please use highrade tubes for V1 and V2.

Check the amp.

If the amp works well, adjust the humpot to best results on
channel 4.

If there is hum or noise coming from the preamp, replace the humpot.

Is there still a problem You need a skilled tech in Your area or send the
amp to Mike at 65amps or Uwe Salwender.

If Your tech needs help, use my email address.

Hope this helps,

Peter
 
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