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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 5:31 am
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Aspiring Musician
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Thank you for the valuable info.
In biasing an amp, is a bias probe sufficient for the job (as per below link), or the ET “Pro One” is necessary?

http://www.eurotubes.com/eurotubes-Bias-Probe-Pro-One-current-watts-voltage.htm

As I am not very technical there is a friend of mine who is ... He is overseas at present and I wanted to get the right gear for the job by the time he is back.

:D


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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 5:52 am
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NT, the EuroTube Bias Probe is nice, because of easy plate voltage reading. You don't need to pull the amp out of the cab to measure this voltage (with output tubes inserted).

If you can spring for it... this bias probe may be a more useful tool. Esp on the road, away from tools or a bench.


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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 6:24 am
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BMW2002Ti wrote:
NT, the EuroTube Bias Probe is nice, because of easy plate voltage reading. You don't need to pull the amp out of the cab to measure this voltage (with output tubes inserted).

If you can spring for it... this bias probe may be a more useful tool. Esp on the road, away from tools or a bench.


The bias adjustment pot is mounted toward the front of the amp behind the tremolo intensity pot. There does not appear to be any external access to the pot. I see no way to bias this amp without removing the chassis from the cabinet.

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 8:18 am
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Bluesky, that can't be correct. All BF and SF amps that have either a bias pot or a balance pot can be adjusted with amp in or out of cab (slots on both sides of pot). There should be a hole with a slotted inset shaft that you can use a small flat screwdriver to adjust with amp in the cab.

The AA165 Pro Reverb has a bias pot.


See "pothole" next to choke?

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 10:25 am
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Ok. The pot access hole is not visible in the OP's photos, but I would love to see the hands of the person that can reach the access hole to safely adjust the bias without removing the chassis from the cab as you implied could be done in your earlier post. I certainly wouldn't want to try it.

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 10:41 am
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bluesky636 wrote:
Ok. The pot access hole is not visible in the OP's photos, but I would love to see the hands of the person that can reach the access hole to safely adjust the bias without removing the chassis from the cab as you implied could be done in your earlier post. I certainly wouldn't want to try it.


+1000!

I can pull a combo chassis out of its cab in about three minutes flat. Any competent amp tech can. Anybody who has an issue with this relatively minor step prior to servicing has absolutely no business putting his dick-beaters inside of a live chassis in the first place.

Arjay

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 11:32 am
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Actually for most Fender amps, it's not too hard to get to. I check the bias on most new cap jobs and/or new output tubes several times before handing the amp back to customers. I find that some output tubes (esp new manufactured ones) can drift about quite a lot in the first few hours of life.

Anyhoo... just place old mitt (I like Mechanix gloves) between the PT and OPT (on top of the choke) and the "pothole" is just behind the choke's mounting screw. My Dad's old Auto Tranny shop had these "complimentary" small screwdrivers with magnet on back end and a nice round plastic grip. They fit the screw's slot perfectly. FWIW.... :lol:


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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 1:24 pm
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BMW2002Ti wrote:
Actually for most Fender amps, it's not too hard to get to. I check the bias on most new cap jobs and/or new output tubes several times before handing the amp back to customers. I find that some output tubes (esp new manufactured ones) can drift about quite a lot in the first few hours of life.

Anyhoo... just place old mitt (I like Mechanix gloves) between the PT and OPT (on top of the choke) and the "pothole" is just behind the choke's mounting screw. My Dad's old Auto Tranny shop had these "complimentary" small screwdrivers with magnet on back end and a nice round plastic grip. They fit the screw's slot perfectly. FWIW.... :lol:


"You're a better man than I am, Gunga Din." :lol: :lol: :lol: :lol:

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 8:57 pm
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"Gunga Din", for sure!!! But, I never had a problem, one way or the other. A 3/16" flat blade, long or short, depending on the amp. Guess, it's the bias probes that make the necessity of pulling the chassis a tech's choice. I mean, that I won't pull a chassis if I'm just playing tube roulette, for the heck of it. JMO, Art

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 9:59 pm
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aclempoppi wrote:
"Gunga Din", for sure!!! But, I never had a problem, one way or the other. A 3/16" flat blade, long or short, depending on the amp. Guess, it's the bias probes that make the necessity of pulling the chassis a tech's choice. I mean, that I won't pull a chassis if I'm just playing tube roulette, for the heck of it. JMO, Art


I could probably fit the bias probe under the power tubes of my Wrecking Ball with the chassis in the cab (the adjustment pot is sticking up in front of the left hold down bolt of the OT), but I'm usually swapping components so its easier just to pull the chassis.

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 10:05 pm
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Herewith how it looks like on the subject amp .. not bad at all.

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 10:17 pm
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Nikola Tesla wrote:
Herewith how it looks like on the subject amp .. not bad at all.

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Good photo.

My concern is, how do you safely get to the adjustment pot to bias the amp with the chassis in the cab. You will have two very hot power tubes sitting about 1" taller (longer?) with the bias probe sockets under them that you have to fit your hand around. Personally, I think it would be better to pull the chassis.

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 10:22 pm
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:D

Hmm... Pulling the chassis out is not a problem at all.
4 screws, that's all :mrgreen:


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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 10:29 pm
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Actually, it's nine screws. Plus unplugging the wiring harness for the speakers and the reverb cables.

Arjay

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Post subject: Re: 1965 Pro Reverb
Posted: Wed Oct 23, 2013 10:53 pm
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Retroverbial wrote:
Actually, it's nine screws. Plus unplugging the wiring harness for the speakers and the reverb cables.

Arjay





Nope.

Actually, its 4 screws in total on mine :mrgreen: :mrgreen:



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