Fender Blackface Vibroverb

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Fender Blackface Vibroverb

Post by Freebird » Sat Jun 03, 2017 5:47 am

Hi forum members

A guitar friend of me will soon bring me an old Blackface Vibroverb amp. I didn't see the amp yet. Referred to his information it is a 63 or 64 model which has a 15" speaker. It seems that it is same SRV has had.

He asked me to have a look at this amp and perhaps to swap tubes or even to recap. Tube swapping I do not worrie about. But recapping I am not shure if it will be necessary. So my question is, how can I detect bad and worn out caps, especially the high voltage electrolytic caps for filtering dc voltage? Does reforming make sense? If yes how can I do that? Is it according to novosibir's method?

What else have I to check on an old Blackface Vibroverb? Any related input is welcome.

Thanks in advance for your help
Daniel

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Re: Fender Blackface Vibroverb

Post by danman » Sat Jun 03, 2017 10:47 pm

Other than looking for obvious physical signs such as bulging or leaking, you really can't test the caps properly without an esr meter or an older leakage tester that will test the cap at full rated voltage. A multimeter will not be of any use in this case. If I owned a fifty year old amp that was as valuable as this, I would certainly feel inclined to replace the electrolytic caps. If one of them fails, it can ruin components and/or transformers.

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Re: Fender Blackface Vibroverb

Post by Freebird » Mon Jun 05, 2017 3:55 am

Thanks danman

Then I'll have to swap all "critical" electrolytic filter caps to keep the amp alive for further 50 years. I'll also have a look at physical signs as you mentioned.

Which electrolytic caps have I to choose for recapping? For example:
- Sprague Atom (http://www.vintagefenderamprepair.com/p ... s-sprague/)
or
- F&T (http://www.vintagefenderamprepair.com/p ... ecap-kits/)?

Daniel

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Re: Fender Blackface Vibroverb

Post by Roe » Mon Jun 05, 2017 7:44 am

try TAD audio series caps made in germany or similar F&Ts. and form them by applying Larry/Novosibir's method
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Re: Fender Blackface Vibroverb

Post by Freebird » Mon Jun 05, 2017 12:35 pm

Hi Roe

Thank you for chiming in and your advice. I'll give TAD audio caps a try, see http://www.tubeampdoctor.com/catalog.ph ... gory_id=79.

I also think that Germans quality will speak for itself. I know TAD products as well, they usually last for a long time.

Daniel

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Re: Fender Blackface Vibroverb

Post by danman » Mon Jun 05, 2017 8:34 pm

I agree...F T caps are my preferred choice for most jobs. Be sure to replace the 25uf bias cap also. If that one fails you could redplate a set of power tubes and fry the OT.

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Re: Fender Blackface Vibroverb

Post by Roe » Tue Jun 06, 2017 8:00 am

Freebird wrote:Hi Roe

Thank you for chiming in and your advice. I'll give TAD audio caps a try, see http://www.tubeampdoctor.com/catalog.ph ... gory_id=79.

I also think that Germans quality will speak for itself. I know TAD products as well, they usually last for a long time.

Daniel
Yes, those German caps are nice but the TAD asian caps seem less reliable
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Re: Fender Blackface Vibroverb

Post by Freebird » Tue Jun 06, 2017 12:07 pm

danman wrote:I agree...F T caps are my preferred choice for most jobs. Be sure to replace the 25uf bias cap also. If that one fails you could redplate a set of power tubes and fry the OT.
Good hint! Don't want a bedside lamp :-) . I then also will swap the bias cap.

Thanks
Daniel

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Re: Fender Blackface Vibroverb

Post by Freebird » Tue Jun 06, 2017 12:14 pm

Roe wrote:Yes, those German caps are nice but the TAD asian caps seem less reliable
Roe, are you referring to the TAD Gold Caps?

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Re: Fender Blackface Vibroverb

Post by Roe » Wed Jun 07, 2017 2:52 am

Freebird wrote:
Roe wrote:Yes, those German caps are nice but the TAD asian caps seem less reliable
Roe, are you referring to the TAD Gold Caps?
yes, those Asian made electrolytics are not very reliable. I've seen a few fail and they don't sound as good as the audio caps or ordinary F&Ts
http://www.myspace.com/20bonesband" onclick="window.open(this.href);return false;
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JTM45 RS OT JTM50 JMP50 1959/2203/34/39

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Re: Fender Blackface Vibroverb

Post by Freebird » Sat Jun 10, 2017 3:31 am

Roe wrote:yes, those Asian made electrolytics are not very reliable. I've seen a few fail and they don't sound as good as the audio caps or ordinary F&Ts
Thank you Roe. Good to know that, I do not have much experience in Fender Amps and their components and favorite brands.

Daniel

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Re: Fender Blackface Vibroverb

Post by Freebird » Sat Jun 10, 2017 3:41 am

In the meantime I got the amp. Looks gorgeous and sounds even with old components pretty fantastic. Also the reverb sounds amazing. Such reverb I miss on Marshall amps sometimes. I have some guts for you, so you get some imagination:

Link to dropbox: https://www.dropbox.com/sh/fy1uup7kduem ... 6Vy7a?dl=0

Some question will come later on.

Have fun
Daniel

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Re: Fender Blackface Vibroverb

Post by Freebird » Sat Jun 10, 2017 4:34 pm

Today I checked the circuit board and found out it is blackface AA763 (not AB763). Because it doesn't have grid stoppers on 6L6 end tubes and some resistors and tone caps are according the AA673 scheme diagram https://www.dropbox.com/s/i6mqddg5nk5v9 ... m.gif?dl=0

Well the speaker of course isn't original. This vibroverb has the well known EVM 15L speaker, which SRV has had for more clean headroom.

I will swap all the filter caps with new 5x 20uF/550V TAD audio caps. Now there are three totem pole networks from an earlier revision in. Also I will mount grid stoppers of 1.5k ohm on pin 5 at both 6L6 tubes, just for safety.

What I do not know is, do I have to swap the brown astron tone caps on the circuit board? Are they prone to get bad over time? The blue molded I think rarely need replacement.

Daniel

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Re: Fender Blackface Vibroverb

Post by Roe » Sun Jun 11, 2017 4:29 am

does it have a 3m3 ir 4m7 in the reverb circuit (in parallell with the 10pf)?
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http://www.myspace.com/prostitutes" onclick="window.open(this.href);return false;
Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

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Re: Fender Blackface Vibroverb

Post by Freebird » Sun Jun 11, 2017 1:05 pm

Roe wrote:does it have a 3m3 ir 4m7 in the reverb circuit (in parallell with the 10pf)?
Hi Roe

It has a 4.7M ohm resistor in parallel with 10pF at the reverb input (and mixer) circuit.

Daniel

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