Update: Herbert - Blowing 500mA fuse for 2&5

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texmarkmusic

texmarkmusic

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I am having a heart attack as I write this. My Herbert has crapped out on me. I am at a loss...I am getting little to no audio passing to the cabinet. Only when I strum hard on the guitar. Using a 16 ohm Marshall cab plugged into the appropriate speaker output. For grins, I pulled the chassis and checked all fuses. Everything looks fine. I decided to pull out my Fluke DMM to check the bias on the tubes...Followed instructions explicitly. Pulled fuse and tested; reading nothing. I checked all three pairs...Nothing!!! Where do I go from here? Who is handling service in the States now? I can't imagine having to ship to Germany for repair.......HELP!

Regards,
Mark Allen
 
You'd have to explain better if you want to get some help. Have you checked your tubes?
 
Sorry about that...Let me get a bit more detailed and I appreciate anything you guys might offer...

In regards to the tubes, I have changed out both the power tubes and preamp tubes...Original power tubes the Ruby EL34's, changed with JJ EL34L's...matched sextet just purchased. Replaced pre with JJ ECC83's. All tubes light up. A simple visual look at the tubes does not point to a problem. Tested all 500mA Slo Blo fuses on the pairs as well as the 2 fuses on the main PCB and the 3rd fuse on the daughterboard...When I say test, I am removing the fuse and doing a visual as well as using my Fluke to measure continuity through the fuse. I am using a Fluke 87 DMM to test mA's. I am pretty familiar with biasing amps. I use a Weber bias probe for biasing my Splawns and my older Herbert. My Einstein is newer and has the same test points for external biasing as the newer Herbert. When I power up the amp, I do set signal, but very little and very weak. Let me know...Last time I had trouble with an Einstein I used to own, the guys at Salwender took care of things. Any word as to who might handle service in the US now in the event I need to have the amp checked by a pro?
I love these amps...I've owned a couple of Einstein's and Herbert's and I am currently GAS'ing for a 2007 or newer VH4...

Thanks again for anything. If I have missed answering anything else, please let me know. I am stumped at the moment...

Mark
 
1. plug guitar into serial loop return. Result?
2. if the problem happened after you've put new tubes into it: try old preamp tubes again. Result?
 
Thanks for the reply...

I just tried plugging straight into the serial loop return with the same results.
Problem occurred before tube replacement. Strange thing is. I am not reading anything when I try to measure milliAmps on any of the three test points for the three pairs. Thanks again for any input you might have. I am willing to try anything.

Thanks,
Mark
 
Please check the voltage on pad "A" on the
3 wires on the outputtransformer. It should be
around 480 volts.

Thanks,

Peter
 
Peter...I am honored by your reply. To make sure I am looking at the correct location, we are talking about the leads that go to the output transformer designated A1 +A, and A2 on the PCB? I should be able to measure 480V at those leads right?

Thanks,
Mark
 
yup. the two outer leads have a bit less volts on them. Red to lead, black to chassis/ground. DMM set to 1000 Volts DC.
 
Just measured....Powered up, Volumes = 0, Speaker load on 16 Ohm

A1 = 515 Vdc
+A = 515 Vdc
A2 = 515 Vdc


Thanks again for the troubleshooting help. You guys are fantastic. This is why I will soon own a VH4 to go with my Einstein and Herbert. Other amp manaufacturers...Take notice to the attention both of these gentlemen have given me...On a Sunday, no doubt......

What should I try next? What is strange is that when I checked, I could not get a reading on any of the three bias test points. Let me know. I am your hands and eyes, Geniuses of Amplification...

Mark
 
Please set DMM to 20V AC (!) and measure the voltage between PIN 2 and 7 of one of the powerubes (heaters)

Then set DMM to 200V DC and read PIN 5 of the powertube socket (bias).
 
Duesentrieb,
Thanks for hanging with me...Here are my readings...

All sockets 2 to 7 are reading appr 6.75 to 6.8 Vac
I tested one socket from each pair on pin 5 and I'm getting a reading of appr -81.5 to -85.0 Vdc


Is that right?

Thanks,
Mark
 
So, I take all the l power tubes out and adjust to -50 Vdc using the bias adjustments on each pair? I want to make sure...Can I get it into that range and will I need to do that on all three? Is there any chance I might have an issue with the bias resistor?

Thanks,
Mark
 
Start with one pot. Set the voltage to -50V (reading on PIN 5). Then put tubes in (just the pair 1/6 or 2/5 or 3/4) and adjust bias.
After you've adjusted bias to 60mA/pair (reading currents at the fuse), reread voltage on PIN again and set the other pots to that. Adjust others pairs currentwise bias.
Your amp should make noise again.
 
Do I need to pull the respective .5A fuse when adjusting @ pin 5? I understand I will have the power tubes removed as well...Do I need to maintain a load on the output transformer (Speaker connected). Let me know....Thanks again for your diligence in helping me troubleshoot this...

Mark
 
Keep the fuse where it is. If master = 0, no load needed.
 
Good Morning Gentlemen...

Here is what I have done this morning...

Removed power tubes,
Set DMM to 400 Vdc, black to chassis ground, red to pin 5.

I powered up the amp and attempted to adjust bias on 1&6 first. Initial reading was -81Vdc. Adjusting bias from the bias point for those tubes, the reading is not changing. I have tried the other pairs as well with same results. I tried several complete turns, but I am seeing no change in the voltage. Is there something common to all pairs that could be the problem?

Thanks again,
Mark
 
Hi Mark,

there's something wrong then.
I'll direct Peter here again to help you.

Olaf
 
Thanks man...I will wait to hear from Peter as to what I might try next...I really appreciate your feedback....



Mark
 
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