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Post subject: Vibroverb reissue just died
Posted: Wed Dec 02, 2015 2:51 pm
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Hi all. Just been playing my guitar and the amp died. No strange noises of any sort. I thought it was the fuse in the plug, but no. It's also not the 1.6A fuse in the back. I opened the chassis and had a quick look. All the fuses look OK too. Anyone have any suggestions?
Cheers
Nick


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Post subject: Re: Vibroverb reissue just died
Posted: Wed Dec 02, 2015 3:49 pm
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Does the pilot lamp light when the amp is switched on?

Arjay

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Post subject: Re: Vibroverb reissue just died
Posted: Wed Dec 02, 2015 3:59 pm
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No. The pilot light is out.


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Post subject: Re: Vibroverb reissue just died
Posted: Wed Dec 02, 2015 4:02 pm
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Hokay.

Unplug the amp, carefully remove all of the tubes, then try powering the amp up again. You won't have any audio of course but that configuration may reveal something about the condition of the power supply. Report your findings.

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Post subject: Re: Vibroverb reissue just died
Posted: Wed Dec 02, 2015 7:43 pm
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How do you check fuse ? With eyes ? Not a good test .

Use a meter


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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 11:18 am
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Amp sorted. I changed the 5at fuse inside the chassis and it's working. Phew!! Hopefully that's the end of the problem. I do now have a tech lined up for future problems. Thanks for your help.


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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 1:47 pm
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Hompie29 wrote:
Amp sorted. I changed the 5at fuse inside the chassis and it's working. Phew!! Hopefully that's the end of the problem. I do now have a tech lined up for future problems. Thanks for your help.


You learn to not trust your eyes to test fuse .

Put the right fuse ,IMO not a 5 amps.


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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 1:56 pm
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Hompie29 wrote:
Amp sorted. I changed the 5at fuse inside the chassis and it's working. Phew!! Hopefully that's the end of the problem. I do now have a tech lined up for future problems. Thanks for your help.


Is this amp the '63 brownface re-issue and are you located somewhere outside the US?

Arjay

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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 2:24 pm
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Yeah the brownface. It's such a great amp. Exactly the sound I've been after for years. Real warm!! I'm in Scotland.
I replaced the fuse like for like. I double, double checked. Yeah the fuse looked fine.


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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 2:56 pm
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stratele52 wrote:
Put the right fuse ,IMO not a 5 amps.


The 5AT fuse is correct for an export brownface Vibroverb. The European schematic shows fuses for each of the secondaries of the power tranny, with the 5AT specified for the heater circuit (which accounted for the unlit pilot-lamp bulb).

Glad the amp's up and running again, Hompie.

8)

Arjay

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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 3:26 pm
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Retroverbial wrote:
stratele52 wrote:
Put the right fuse ,IMO not a 5 amps.


The 5AT fuse is correct for an export brownface Vibroverb. The European schematic shows fuses for each of the secondaries of the power tranny, with the 5AT specified for the heater circuit (which accounted for the unlit pilot-lamp bulb).

Glad the amp's up and running again, Hompie.

8)
Thank's for the answer
Arjay


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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 4:38 pm
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One more thing you may want to check, before going out and gigging... the idle bias of the output tubes. One or both maybe hogging current. With 425-450VDC on the plates, should have idle current around 35-40mA per each tube.

Good luck. Keep some proper spare fuses taped to inside of cab.

:mrgreen:


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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 6:02 pm
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There is no adjustable pot for the bias circuit on account of the bias-wiggle tremolo circuit -- it's nearly identical to that of a Princeton or Princeton Reverb.

Arjay

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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 7:02 pm
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Retroverbial wrote:
There is no adjustable pot for the bias circuit on account of the bias-wiggle tremolo circuit -- it's nearly identical to that of a Princeton or Princeton Reverb.

Arjay


Ugh! That is no good. Well, at least measure idle bias current --- in case one tube (or both) is way off nominal value. I guess one would need to buy GT "rated" output tubes, similar to what is OEM in the amp? Or play with set resistors. Or put in a bias pot (best long-term solution).


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Post subject: Re: Vibroverb reissue just died
Posted: Thu Dec 03, 2015 8:32 pm
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BMW2002Ti wrote:
Ugh! That is no good. Well, at least measure idle bias current --- in case one tube (or both) is way off nominal value. I guess one would need to buy GT "rated" output tubes, similar to what is OEM in the amp? Or play with set resistors. Or put in a bias pot (best long-term solution).


The original 6G16 lacked a bias-adjustment pot as well. More than anything else, this amp was a "test mule" for what would later come. Likely the reason that only some 405 brownface Vibroverbs were made.

Arjay

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