VH4. Power amps changed, now pre amps.... Question???

  • Thread starter Thread starter Axegrinderturbo
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Axegrinderturbo

Axegrinderturbo

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Hey,

I received my matched quad of winged C EL34's yesterday and put them in today, sounds amazing!!! Just a question regarding the pre amp valves........ they've never been changed an i've had the amp for about 3 years and use it 3 times a week full volume. I found 2 new Mesa 12AX7's in our rehearsal room today and I was wondering if I could change 2 out of the 7, or if you would just waiting and changing the full set?

I predominantly use ch.3 so what positions would you recommend putting the 2 new valves into? The last thing I would want to do is damage the amp so if this isn't recommended then i'll leave it.

Also......... if the front is facing me, is it V1 - V7 left to right?

Thanks!

Stu :rock:
 
If im not mistaking there is no problem in changin some valves and not others in the preamp, you'll might not even notice some of the changes so you might be wasting it. I would just change the set and get done with it if I were you.

And yes the V1 is the position from the left when standing in front of the amp. If you were to open it from the back it would be on your right side.
 
I think I'll just leave it and just replace the set, not too sure what to for yet but I'll do a bit of research.

I was going to go for the 6550's but I got chance to try them and I preferred the el34 =c=, also Diezel recommended them aswell helped ;) I'm so pleased withe sound though, was starting to loose a lot of volume with the old tubes!
 
Axegrinderturbo":3dgfo06b said:
I think I'll just leave it and just replace the set, not too sure what to for yet but I'll do a bit of research.

I was going to go for the 6550's but I got chance to try them and I preferred the el34 =c=, also Diezel recommended them aswell helped ;) I'm so pleased withe sound though, was starting to loose a lot of volume with the old tubes!
Click to expand...
:aww: Well, as long as you're happy with 'em Bro... I think the 6550's are the tits with the VH4's personally - regardless of what the brass say.

Best,
V.
 
Does the amp sound good? Is it not suffering from any noise? If the answer is yes to both then I would just leave the preamp tubes alone. Preamps last a lot longer than power amp tubes.
 
Yeh it sounds great and there is no noise that you wouldn't expect. For piece of mind I think I'm going to change them all and get them ordered in a couple of weeks!
 
Had a nightmare today!!! I changed that power amp valves on Friday evening (=c= matched el34 quad) and took the amp to our rehearsal room on Saturday morning. I had problems with my multimeter as it wasn't reading anything so I was unable to bias the amp but it sounded awesome.

I borrowed another multimeter today an tried to take another reading at lunch today however it still wasn't reading anything (to be fair it didn't look the newest multimeter ever!) but I didn't crank the amp up as I didn't have time. I got to rehearsal this evening an the amp was so quiet I couldn't believe it, no power behind the sound at all, very quiet across all channels. I took all of the tubes out (including pre amp) and put back in which made it a bit louder but not the sound I experienced on Saturday! Sorry if this sounds a bit rambly and not coherent, but my thoughts are:

Problem with the amp as no tube fault lights illuminated and all tubes are glowing fine
Could I have caused damage by not biasing?
Should I change all pre amps before anything else?

** One thing I didn't mention was the multimeter I initially tried does not have the clips to connect the the OT, it's just metal spike at the end. While trying to bias I had the black on wire to the primary and the red slipped off and touched the metal casing of the amp and made a small clicking sound. The amp worked fine initially after this but I though it may be worth mentioning **

I think I may give James at Diezel UK a call tomorrow and price up how much it would be to send it down........ worse case scenario that is ;)

Stu
 
Sorry to read this Bro... But let me tell you something straight up. DO NOT F*CK with your amp any more!!! Take it someone who knows what the hell they're doing...!! The mere fact you didn't even bias your amp yet tell us that it sounded awesome and all leads me to believe you don't really kinda totally potentially know what you're doing....?!

So don't f*ck with it anymore. Yanking out pre's and power valves isn't going to fix any VOLUME problems dawg. That's just erred thinking. Ya need a tech! Ya need a TRUE re-bias, and once it's said and done - DO NOT F*CK with the back of that amp ANYMORE!! Stick the lead in the front and stay AWAY from the back of it...

Peace,
V.
 
Thanks for the replies. To be honest I have biased the amp before without any problems so I wouldn't say I'm f**king with the amp but I understand the point being made. I absolutely love the amp and look after all of my gear and would never approach anything thinking I may possibly damage my equipment.

I'll be giving Diezel uk a call tomorrow and probably just send it to them for piece of mind.

Stu :rock:
 
You most likely blew the fuse in the multi meter with your slip, hence it's not reading.

Before you proceed to spend money on a tech, try a few common sense repairs first. Go buy a new fuse for the multi meter and some
crocodiles. Check the bias, so that it is not into cutoff then if it still does not work check the internal
fuses for continuity with the amp off and finally the preamp tubes used for all channels.

The logic is you will spend ￡80 to ship it off, but you won't spend ￡5 to get what is required to do it yourself.

VH4:
V1 Used by all channels
V2 Used by channel 4
V3 Used by channel 2/3/4
V4 Used by all channels
V5 Mixer and Send buffer
V6 Return driver
V7 Phase Inverter
 
Many thanks for the reply,

It sounds like the amp is running at half power at the very most, doesn't sound particularly bad, just not much power behind the sound. Does this sound about right for the cut off mode? Also when I bias the amp correctly will it automatically come out of the cut off mode?

Thanks
 
Consider the high bias is a gas pedal at 90% throttle. How much further can you go ?
 
The 500ma fuse had blown in my multimeter and so this was changed and the bias was set to 60ma. It was around 75 before I changed it so I'm guessing this was the cause for the power cut. With the bias set it's working great!

This may sound like a strange question but what volume settings would you expect to use for a rehearsal with a loud drummer, nothing micd up. I have the ch3 volume to around 11 o'clock and the master to around the same, this seem reasonable?
 
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