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PostPosted: Wed, Dec 06, 2017 3:05am 
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Hack

Joined: Sat, Dec 02, 2017 4:24am
Posts: 5
(Well, I can't seem to figure out why Rig-Talk won't let me log in with my actual account and wants me to solve a reCAPTCHA that doesn't seem to exist, but anyway.. I suppose this alternate account with an underscore in it should work just as well...)



So, a few months ago (August) some members here helped answer a few questions for me (viewtopic.php?f=14&t=190847) and, after 8 years of Einstein ownership, I tracked down what I was looking for and expanded my arsenal with this:
Image


Wow! This is definitely an amazing sounding amp!! :rock: ..and even better with the brand new set of power-tubes I just swapped into it.

I'm enjoying everything about the Herbert, however, I'm experiencing an above-average amount of hum in the amplifier's output (similar to ground-loop hum, but it doesn't appear to be that). I haven't had any luck eliminating the hum, but while I was re-tubing & biasing it.. I took it out of its headshell to try the hum-trimmer pot (also unsuccessful), and noticed this:
Image

Image

I'm curious if these two leaking capacitors might be causing the hum that I am experiencing in the Herbert's output?
Also, how hard would it be to replace them? / Would the brand make a difference? / What values are required?



That said / in other related craziness -> I also just grabbed this for good measure:
Image


Also an amazing sounding amp!! Different, but still obviously the same underlying DNA... and between the two of them I literally can't stop smiling :D :D :D :D
Craziness, I'm ridiculous.. totally don't regret it though.


No issues at all with the sound or operation of the VH4 (I'll probably re-tube it soon either way), but I did notice that at least 2 of the large capacitors located just in front of the power tubes appear to be bulging at the tops.
So.. same questions I suppose: How hard would it be to replace them? / Would the brand make a difference? / What values are required?


Thanks in advance for any answers / advice on the cap questions.. I'm super stoked nonetheless!


:thumbsup:


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PostPosted: Wed, Dec 06, 2017 1:23pm 
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Plank Cranker Trainee

Joined: Tue, Dec 04, 2012 12:34pm
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Congrats!

The required values are specfied on the capacitors themselves,
The have a polarity. Do not forget that. A tech could easily replace them.
Personally, I am not fond of people buying a cheap soldering iron and then immediately starting to learn how to grill the circuit board of a 4000$ amp iykwim.

Does the hum come out of the speaker cab or only from the amp itself?

The transformer in my vh4 hums even with the standby off, but that does not affect the sound that comes out of the cab.
I guess your hum is due to defective caps and can be heard through the cab.

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PostPosted: Wed, Dec 06, 2017 1:48pm 
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Hack

Joined: Sat, Dec 02, 2017 4:24am
Posts: 5
Thanks for the response.

I'm still on the fence regarding whether or not I'd attempt to replace the caps myself, or find a tech do to it (my soldering work is typically relegated to cables, wiring rack rigs, patch-bays.. that sort of thing. Circuit boards are not something I would typically be working with.)

Regarding the Herbert's hum: Yeah, it is coming out of the speaker cabinet. The amp does have a decent amount of transformer hum I suppose, but I'm only concerned with what comes out of the output.
Both amps could stand to have some caps replaced, but only the Herbert is making any unwanted noise.


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PostPosted: Thu, Dec 07, 2017 2:45am 
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Diezel Amplification
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Joined: Sun, Jul 02, 2006 5:43am
Posts: 4690
There is a chapter in the service manual on our website.
Please read it.


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PostPosted: Thu, Dec 07, 2017 3:38am 
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Hack

Joined: Sat, Dec 02, 2017 4:24am
Posts: 5
Peter Diezel wrote:
There is a chapter in the service manual on our website.
Please read it.


Thanks for the reply Peter!
So I read the section in the service manual. It definitely appears to be the 22mf/500V caps in the Herbert which are leaking.
I do have a couple of questions:

1) Does it matter what brand of capacitor is used for the replacement?
2) What type of glue should be used to glue the new ones down?


Lastly, what are the values of the big ones located in front of the VH4's power tubes. I can't make out the writing through the front grill and I would like to be able to order the parts before I take the amp out of its headshell.


Thanks again. :)


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PostPosted: Thu, Dec 07, 2017 4:45am 
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Plank Cranker Wanker
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Joined: Sat, Dec 09, 2006 1:06am
Posts: 1412
Location: Granite City, IL
The VH4 ones are most definitely fine as long as you can press on the tops and they aren’t hard(they push in a little)it’s just the tops of them separating and not an issue. The other question is just regular old hot glue from a glue gun and as long as they’re in spec it’s only smoothing the power and isn’t so much a sonically sensitive part other than value.


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PostPosted: Thu, Dec 07, 2017 5:54am 
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Diezel Amplification
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For both questions is doesn´t matter.

Be sure to replace the 2k2 filter resistor into 4k7 / 5 watt. This will save the new caps.


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PostPosted: Sat, Dec 09, 2017 3:11pm 
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Hack

Joined: Sat, Dec 02, 2017 4:24am
Posts: 5
Thanks for the responses and information :)

www.thetubestore.com sells F&T caps with the right values so those should be easy enough to get. (I'm in Canada and near enough to them.. so it's the easiest/fastest source).

I might have to do some searching and call around to find a resistor with that value. There aren't too many electronic parts suppliers around anymore and so it could come down to online ordering or driving a city or two over.


Either way, I look forward to cleaning up those couple of caps and the reduced noise that should come along with doing so.


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