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Post subject: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 3:38 pm
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I recently bought a second-hand 1981 Pro Reverb silverface. This is the 70 Watt ultra-linear version, not the older 40 Watt version. However, after a week it suddenly wouldn't turn on anymore. I checked the fuse and it was blown. I replaced the fuse, but the amp still wouldn't come on and the fuse was still OK after trying to turn it on.

This amp has a voltage selector (100-260 V) and I found that after switching the voltage from 240 to 220 Volt it would turn on again!

Someone told me that the power transformer probably died somewhere between the 220 and 240 Volt points, which would also explain the blown fuse. Does this make sense? Sadly I'm not too good with electronics myself.

The power outlets where I live provide somewhere around 230 Volt these days. Is it OK to use this amp set to 220 Volt, or will I ruin this amp and will I need to get this transformer replaced?

I e-mailed an amp repair shop and they told me a replacement transformer would probably cost me around €250, not including shipping costs and installing it. I guess the total amount will probably work out to more than half of what I paid for this amp...

I have been searching for a replacement power transformer online myself and I found a couple of brands that offer replacement power transformers for the Pro Reverb (part number 125P5D & 022798), but they all seem to be either fixed 120 VAC 60 Hz or 240 VAC 50 Hz units, while my amp has a 100-260 Volt selector switch.

I found these power transformers that list they can be used for Pro Reverbs:


Will I be able to use a 125P5D replacment transformer like that in my ultra-linear 70 Watt Pro Reverb? If so, any comments on which one to get? If not, what part number do I need to look for for my amp?

(The Hammond 290DEX is just over €100, so that would be a lot cheaper than what the amp repair shop I e-mailed is offering...)


Last edited by breun on Tue Nov 08, 2011 4:53 pm, edited 2 times in total.

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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 3:52 pm
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Yeah, it sounds like the PT has issues somewhere in the outer windings (240-220 VAC range).

Remember, you need a PT that can handle your 70 watt amp (enough mA rating). And you need 50Hz type. Or 50/60 Hz type. NOT 60Hz only. Prolly the 250 VAC/50HZ is what you need.

But before spending that $$$, maybe good to look through the amp for other potential problems which may have caused the original PT and fuse to blow, in the first place. Like how old are those filter caps in the power supply?


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 3:55 pm
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The 125P5D power tranny will not supply sufficient voltage for an ultra-linear Pro Reverb -- its B+ tap is only 440VDC, the UL chassis requires 500VDC.

In your circumstance, I'd recommend the Hammond or a Merc-Mag replacement with US specs (ie: 125-volt primary) and find yourself a stand-alone outboard matching transformer. Thus, it could conceivably used with other US-spec gear you may have.

HTH

Arjay

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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 4:09 pm
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BMW2002Ti wrote:
Remember, you need a PT that can handle your 70 watt amp (enough mA rating).


I don't know what the mA rating for this amp is. Do you mean a 125P5D replacement transformer won't cut it? The Hammond 290DEX PDF says "Exciting current: @240V, 50Hz, BLK - BLK = 266mA Max." and "Sec. Voltage (RMS): 650VCT @ 230mA C/W 50V TAP, 5V @ 3A / 6.3VCT @ 4A". These are the only two specs that mention a mA value, but it's mostly Chinese to me.

BMW2002Ti wrote:
And you need 50Hz type. Or 50/60 Hz type. NOT 60Hz only.


Yeah, I got that.

BMW2002Ti wrote:
But before spending that $$$, maybe good to look through the amp for other potential problems which may have caused the original PT and fuse to blow, in the first place. Like how old are those filter caps in the power supply?


I'm not sure, but I don't believe they're original. The guy who sold this amp to me said it had been checked out recently and once had a bunch of parts replaced, but I don't really know about the details.

Thanks for your reply.


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 4:27 pm
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Yeah, it's looks like the 290 DEX or EEX is the Hammond replacement tranny you need. Does your amp have this schematic?

http://www.webphix.com/schematic%20heav ... tr_rev.pdf


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 4:49 pm
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Retroverbial wrote:
The 125P5D power tranny will not supply sufficient voltage for an ultra-linear Pro Reverb -- its B+ tap is only 440VDC, the UL chassis requires 500VDC.

In your circumstance, I'd recommend the Hammond or a Merc-Mag replacement with US specs (ie: 125-volt primary) and find yourself a stand-alone outboard matching transformer. Thus, it could conceivably used with other US-spec gear you may have.


I have no US spec gear, I live in the Netherlands. You're saying a 125P5D won't work? BMW2002Ti says it will. I'm confused now. If a 125P5D replacement transformer won't supply enough voltage for an ultra-linear Pro Reverb, then what's the part number for the transformer I need? Or what are the specs I need to look for?


Last edited by breun on Tue Nov 08, 2011 4:51 pm, edited 1 time in total.

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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 4:50 pm
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BMW2002Ti wrote:
Yeah, it's looks like the 290 DEX or EEX is the Hammond replacement tranny you need. Does your amp have this schematic?

http://www.webphix.com/schematic%20heav ... tr_rev.pdf


Yeah, that's the schematic for my amp. Where in this schematic do you find what the transformer specs are?


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 5:13 pm
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Your are better to find a good tube amp tech wich he will do a complete checkout ouf your amp and is power transformer before buying a new one.

If needed he should be able to ordered the proper replacement


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 5:21 pm
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I agree with Stratele, you should have the amp power sections (power supply and power tubes) checked out thoroughly, before plopping that heavy iron into the amp.

To be sure what Hammond tranny to use email Hammond with the OEM part number: 013895 BN


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Tue Nov 08, 2011 7:01 pm
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stratele52 wrote:
Your are better to find a good tube amp tech wich he will do a complete checkout ouf your amp and is power transformer before buying a new one.

If needed he should be able to ordered the proper replacement


+1!

"The guy who sold this amp to me said it had been checked out recently and once had a bunch of parts replaced, but I don't really know about the details."

Make sure the next tech you take the amp to isn't the same one who last worked on it.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Wed Nov 09, 2011 2:19 am
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I understand that taking the amp to an amp tech is the best solution, but I'd like to get to know more about this stuff myself and I'd like to make sure that I don't spend more than half of what I paid for this amp on getting a transformer replaced if that isn't really necessary. I hope you understand that I'm not very happy that the amp broke down only a week after I bought it.

Anyway, thanks for your help so far.


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Wed Nov 09, 2011 4:58 am
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You said on your first post that your outlet power voltage is 230 volts and the amp is now working if selector is at 220 volts.

What is the problem ? Voltage selection is alright.
Here in North America, we have 120 volts power outlet and we use old Fender Blackface amp which are desing to work at 110 volts ( 1950/1960 voltage ) with no problem. Same for your amp. Forget replacing power transformer.

Leave the amp like that and enjoy it. It would be a good idea to test bias voltage on power tube and readjust it IF needed.

Can you send us a few pictures of your amp wiring, power transformer... this could give an idea if it is modified.
And you could take your time to find a good tech just in case you needed later. If you have somes questions you are welcome.


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Wed Nov 09, 2011 5:55 am
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stratele52 wrote:
You said on your first post that your outlet power voltage is 230 volts and the amp is now working if selector is at 220 volts.

What is the problem ? Voltage selection is alright.


Other people I asked, including a tube amp tech, told me that this is not alright. The problem is that I don't know who to believe.

Another amp tech I e-mailed about this problem thinks the problem is in the voltage selector and thinks the transformer is OK. I think I'm going to look into that first now. That would probably make this whole issue a lot simpler (and cheaper to fix, I guess).


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Wed Nov 09, 2011 6:15 am
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Sure , you check voltage selector if it working properly.

It is well established and documented that the old fender amp was built to operate at 110 volts for 40 years and that they use in 120 volt safe.
If your transformer is ever defective with this use, you will not have the choice to replace him.
What my point of view and with the information you give us will not occur.


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Post subject: Re: Pro Reverb silverface 1981 power transformer problem
Posted: Wed Nov 09, 2011 12:27 pm
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I contacted Mercury Magnetics and they told me the PT for the 70 Watt ultra-linear Pro Reverb is #013895, which is pretty different from the one used in the 40 Watt Pro Reverb.

They also told me that whether running the amp on 220V is a good idea depends on the actual voltage coming out of the wall socket. Here in the Netherlands we get 230V from the wall sockets, but it could be really 227V or it could even be 237V. If it's on the high end you're going to burn tubes and maybe even fry the PT.

Using a 240V PT would be a good thing according to MM because the tubes would run a little more relaxed and sound a little better too.


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