vh4s problem! please help

  • Thread starter Thread starter LanierP
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LanierP

LanierP

Active member
Hey Guys,
I have had my VH4s for about 6 months. Bought it off ebay. I run it thru 2 mesa halfbacks (4x12) and have loved the sound of all channels etc..very happy, but then came a problem. Came home for lunch one day to jam out a little and turned her on..the lights all come on but no sound at all..dead..zero volume..so I took it to a local tech dude..he said there was an issue with the rectifier or something..anyways 2 days later he had fixed it..I brought it home but now the amp has about half the volume that it should...I know this thing is only 50 watts but I know it was much louder when i first got it. The tech did say that the power tubes in it were cheap chinese tubes. The tubes have not blown(all the lights are on for the blow leds on the back) and i can actually see the power tubes thru the back of the chasis and the are lightly lit and seem to be alright (i know what a blown or about to blow tube looks like). any suggestions??? should i try new power tubes? Channel 1 aND 2 i can crank the volume on each and then crank master volume all the way up and play away and still be able to have a conversation with my buddy...based on what i heard this baby do when i first got it..volume is down about 40%...any suggestions would be helpfull. Thanks
 
Could be a bad V1 or a blown/bad hum trimmer. I think you were hosed with the whole rectifier issue. There are two, one for the HV and one for the heaters to the preamp.
Which one did he change and do you have pics ?
 
Please check all tube fault fuses, also when the indicator
LED doesn´t light up. If they are blown, replace them and
test the amp. If the fuses get blown again You need a
quartet of new power tubes.

Please try to get "cheap Chinese" EL34BHT from Ruby Tubes.
They sound good and are reliable. That´s my small
opinion after replacing and insert about 40000 power tubes
(knocking on wood).

And ...... listen to Mark2C ;)
 
who can argue with the master! I will take your advice and try replacing the power tubes with "cheap Chinese" ones. i will do this tonight and let you know what i find. Thanks very much for your time Peter. It is much appreciated
Lanier
 
LanierP":2ppb4ia2 said:
who can argue with the master! I will take your advice and try replacing the power tubes with "cheap Chinese" ones. i will do this tonight and let you know what i find. Thanks very much for your time Peter. It is much appreciated
Lanier
Click to expand...

Please try a new V1 first, V4 and then power tubes since it will be out of the chassis for a bias.
No V1 or V4, no output anywhere. When you power up make sure you see the tubes light up. The heater filament
glows orange. If you don't see this your hum trimmer could be blown or shorted. Since you have not blown any tubes or fuses it should be fine.
If you need any assistance with the location of the hum trimmer or a bias tutorial let me now and I will post whatever you need.

What I like the most about Papa Diezel are his ears !!!!! EL34BHT's sound great.
 
Just to follow up...I put a new quartet of J&J tubes in the amp last night and nothing was changed..still very light on the volume..so i dont believe that it is a power tube issue. Also I noticed that both master volumes for either side basically dont add any volume from 12oclock on the nob( straight up) all the way to wide open.... there is no difference in volume from those 2 positions... also i was wondering what you were refering to by V1 and V4??? the preamp tubes??? keep in mind that I have a ton of time playing with amps on the outside and very little on the inside... I have a fear of getting zapped!!! guess i will take it to the shop here and see whats up...discouraged here :(
 
LanierP":1nfjkhzh said:
Just to follow up...I put a new quartet of J&J tubes in the amp last night and nothing was changed..still very light on the volume..so i dont believe that it is a power tube issue. Also I noticed that both master volumes for either side basically dont add any volume from 12oclock on the nob( straight up) all the way to wide open.... there is no difference in volume from those 2 positions... also i was wondering what you were refering to by V1 and V4??? the preamp tubes??? keep in mind that I have a ton of time playing with amps on the outside and very little on the inside... I have a fear of getting zapped!!! guess i will take it to the shop here and see whats up...discouraged here :(
Click to expand...

I think that Mark said V1 and V4 preamp tubes because V1 and V4 are used by all channels in the VH4.
V1 is the first position from left facing the amp.
 
You won't get hurt replacing a preamp tube and it's not necessary to ship the amp to have replaced.
From the back of the amp, the V1 is behind the output transformer. From there, go left to V2-V7.

Here is a tube task list from the Diezel web site.

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

In the layout below follow the labels. It is a bit easier to replace the preamp tubes if the chassis is out
until you get a feel for how the pins are lined up .

V1V7.jpg
 
Well guys, I tried my best but it looks like there is something else wrong with my amp other than tubes. I tried replacing v1 and v4 as recommended and the was no change. I didnt think there would be since the preamp tubes seem to light up normally all across the amp. I did take it out of the chasis and snapped a few low quality pix with my phone. Channel 1 actually start to distort a bit when i have its volume turned all the way up and the master turned all the way up and it still is about as loud as my 80$ crate 15 watt pratice amp...actually the crate may be louder and it has 1 8" speaker vs 8 x 12's im running the vh4s thru..basically trying to give u guys an idea on how weak the volume level is here..channel 2 volume is even lower...not sure what to do now...ship it to you guys or try the local tech nerd....any suggestions....here are some pix of my amp
 
Those rectifiers look stock.

I did not post the VH4S tube layout.

VH4S:
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 1
V7 Return driver 2
V8 Phase Inverter 1
V9 Phase Inverter 2

Try a new V6 and V7 and the V8 and V9. Don't give up that easy.
Your getting some signal to the power amp so it most likely preamp tubes
or a bad filter cap for the preamp.
 
Tried fresh tubes all across the preamp board and its the same...it just doesnt have the volume..i tried to video this so that you can see what im talking about. note that the volumes on every channel are all the way up and the masters are also all the way up...its as loud as it goes...and its not that loud...at a total loss...this is getting me a bit down...what video formats are allowed to post on here..it wont allow my 30 second clip in asf format...wma and all others are over the 2 meg limit... :no: i guess to the shop she goes :doh:
 
You may want to be a bit more informed before you take it to the shop. It's better to tell a tech where to look than
give him a blank check.

Before you even go, check these fuses !!! Replace them before the tech ever gets the amp.

oldfuse.jpg


If still no volume, tell the tech:

A. The amp has plate voltages of around 477
B. Look at the voltage on the 50uf/500V cap that connects to the end of the preamp board
C. Check that the 2.7K dropper resistor is good.
D. Check for voltages of 477 at the other two 50uf/500V filter caps.
 
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