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Post subject: 65 Pro Reverb with weak reverb
Posted: Thu Jun 20, 2013 9:10 pm
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Hi all.

I'm hoping someone with experience can help a guy out.

I own a 65 Pro Reverb. Bought it used nearly 30 years ago and it wasn't in great condition then, but I want to put away my 92 Princeton Chorus and get the PR back out. I have had the tubes and sockets replaced and it's still very strong but now it started with the hissing noise. I'm sure the resistors and caps are well in need of replacing, and I can handle that, but my real concern is the lack of reverb. I have almost none unless I have it cranked to 5 or more and even then it's not much.

Can someone tell me what would cause this? If it's just caps and resistors then I will move ahead with that, but if I need to look elsewhere I would like to know before I start digging.

Thanks!


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Thu Jun 20, 2013 10:23 pm
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The V3 and V4 tubes are, respectively, the driver and recovery stage for the reverb circuit. If either of those tubes is marginally-performing, the result may cause the symptoms that you describe. Locate them using the tube chart on the inside of your cabinet (tubes are ordered from right to left) and try replacing them with known good bottles. You'll need a 12AT7 (V3) and a 7025 or 12AX7 (V4).

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Fri Jun 21, 2013 12:33 am
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Nice amp, Randy!! Arjay hit on the tubes. (+100) You might want to make sure the RCA plugs and jacks, from the tank, are clean. If you can check; the tank's output ohmage should be near 200ohms, the input ohmage should be near 10ohms. Just a note; if you're getting a good spring splash, when jarring the amp, the input side of the circuit would be the first place, I'd look for faults. JMHO, Art

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Fri Jun 21, 2013 5:07 pm
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You guys are great! You're direct, specific and get right to the point! I'll get started this weekend, and thanks for the impedance tip on the reverb tank.

I picked it up cheep in a pawn shop back around 78-80. I've used other amps but now it's time to break out that aged tone.


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Fri Jun 21, 2013 6:06 pm
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It doesn't get much better than a '65 Pro Reverb!

8)

Post some pics if you get a chance.

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sat Jun 29, 2013 7:56 pm
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Well I had some time to do some digging this weekend and found out a few interesting tidbits. I checked the date again and verified it is a 65, at lease according to the net.

It also has a bad filter cap which looks original. I have 2x 70u@350v, 3X 20u@500v. Also tested the 6L6's with a laser thermometer and one was 210f and the other was 280f. The rectifier tube also has a hot spot on it but glows orange. The reverb pan was tested with a cheap multimeter and showed open on the input. No resistance at all. Here's a few pics I took during my first trip inside...

Image

Image

Is this just transformer "sweat" or something worse?
Image

And finally the rectifier tube with the dark spot. All tubes were orange and I didn't bother turning t up past 3 for the test but I didn't see any arcing or hear anything odd, other than the constant hiss from the speaks.
Image

This amp is in serious need of some TLC. The previous owner swapped the speakers and one is a 16 ohm Celestion G12M and the other doesn't have a name but the part number Googled up an 8 ohm Pyle instrument speaker.

So now I have questions! :wink:

What's a good source for parts, especially the filter caps? Any suggestions for the hissing noise or should I swap the caps first and go from there? Oh yea..... those speakers will be replaced. Not sure what with but they are coming out.

Many thanks!


Last edited by Randy70065 on Sat Jun 29, 2013 11:26 pm, edited 1 time in total.

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sat Jun 29, 2013 8:25 pm
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First up, that rectifier tube does not appear to be a GZ34 (specified by the circuit design and the tube chart). And it looks pretty toasty to me. Start with a fresh GZ34.

The OEM filter caps are bleeding electrolyte -- well past due for replacement. I recommend F&T's for their reliability and longevity. While you're under the doghouse, check all the resistors on the power rail for any signs of component drift or thermal damage. Replace with identical values (do not over-spec them). I recommend metal-film types for their resistance to thermal damage.

Replace the electrolytic in the bias-supply circuit (use an F&T there as well) then check all related components for serviceability. Inspect (and replace if necessary) any leaky bypass caps on the circuit board but leave the tone caps alone.

If not already so configured, replace the original power cable with a modern, grounded 3-conductor type with the hot (white) lead wired to the on switch, then disconnect or remove the death cap which will no longer be needed.

Install a matched set of serviceable power tubes then bias the amp to spec (33 to 38 mA would be good starting point depending upon what power tubes you've installed).

You'll need a pair of 8-ohm speakers, wired in parallel. OEM types would've been the Jensen C12NA, the Oxford 12M8, or a similar-spec Utah. You may vary the brand based on your sonic preferences but they should each be 8 ohms for optimum efficiency and safety.

You'll find most of what you need on Ebay.

Best of luck

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sat Jun 29, 2013 11:32 pm
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Retroverbial wrote:
First up, that rectifier tube does not appear to be a GZ34 (specified by the circuit design and the tube chart). And it looks pretty toasty to me. Start with a fresh GZ34.

Arjay


Yep. I don't know who put that light bulb in there. I thought something was wrong when I saw how it didn't look like the tubes I was pricing. Already ordered a new one.

I got this from a pawn shop. The guy at the store said his son worked on it so they could sell it. No telling what was done to it. The inside looks untouched from what I can see.

Thanks for the advice!


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jun 30, 2013 3:44 am
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Retroverbial wrote:
...replace the original power cable with a modern, grounded 3-conductor type with the hot (white) lead wired to the on switch...


White is neutral, black is hot. Sometimes it is easier to put the white to the switch and the black to the fuse, I've done it so as to keep the accessory outlet wired as-is and not to have to rewire it. If the accessory outlet has one slot wider than the other, be sure that the wider slot is connected to the white of the power cable. :idea:

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jun 30, 2013 10:04 am
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Mea culpa, shimmilou is correct.

:oops:

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Mon Jul 01, 2013 8:05 pm
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I'm searching for parts now but having trouble finding the exact capacitor values. How important is it to use the exact values? Triode USA says "Use 80 uF 450V or 100 uF 350V if you are trying to replace the 70 uF 350V capacitors found in Fenders". Other sites and some YT clips on amp repair say stick with the same values, and I would if I could find them, but finding F&T or Sprague with the exact values as the ones I am replacing is proving more than difficult. Not sure if it means much but I prefer not to mix brands.

As far as keeping the amp original.... the sound yes, but with regard to the value or devalue of the amp based on what parts I use it's not a huge deal to me because I've had it in the closet for 30 years and don't see it going anywhere anytime soon.

Thanks!


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Mon Jul 01, 2013 8:36 pm
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Yeah, the 80uf 450VDC should be fine. Art

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Mon Jul 01, 2013 10:28 pm
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aclempoppi wrote:
Yeah, the 80uf 450VDC should be fine.


+1

As used in the filter array, the value change will have minimal sonic effect on the amp's overall tone. Increasing the cap values *may* tighten up the bass response a skosh.

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Tue Jul 02, 2013 8:43 pm
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Randy, hold on to that rectifier tube. I'm guessing it is a high quality 5URGB. The metal base and ST glass envelope tell me it's from the late '50's or '60's. I may be wrong!!! But maybe Beemer can give a better assessment of that tube. Art

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Tue Jul 02, 2013 8:57 pm
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aclempoppi wrote:
Randy, hold on to that rectifier tube. I'm guessing it is a high quality 5URGB. The metal base and ST glass envelope tell me it's from the late '50's or '60's. I may be wrong!!! But maybe Beemer can give a better assessment of that tube. Art



I set it aside figuring I would make a nightlight out of it when I run out of things to do. I'll hang on to it. Thanks, Randy


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