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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jul 07, 2013 12:53 am
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BMW2002Ti wrote:
Randy, try a good contact cleaner (I like DeOxit GN5 or D5) on the sockets and pins of the tubes. This often solves hiss and popping issues.


Also a similar symptom as when an aging carbon-comp resistor becomes porous and absorbs moisture......

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jul 07, 2013 3:38 am
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+1 on the carbon-comps

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jul 07, 2013 5:25 am
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Wooden chopstick tapping the components may help you find noisy resistors or a bad solder points. Be sure amp is on a stable platform while doing this test. Don't grab the amp with your other hand while doing this test.

I find that if the amp has been sitting in storage for a long time, CC resistors can absorb moisture & become noisy. A liitle heat from a hair dryer can sometimes help dry them out. Just a thought.

Good luck!


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jul 07, 2013 7:32 pm
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Thanks for the tip BMW - I tried the dryer for a couple of minutes before putting it back together. Something helped... I got some reverb back!!

I swapped the one bias cap, resistor and rectifier tube that came in yesterday. It still hisses but not as much as before and the reverb is present at all volume levels, whereas before I had to turn the volume past 5 to get any r-verb.

I'm hoping the amp will continue to improve once I get the rest of my caps in. Sure wish sites would say upfront if they don't have the parts in stock.

I poked it all over with a stick and didn't find anything odd, except for one of the blue caps on the far end opposite of the PT. I can hear my tapping just slightly through the speakers.

The rectifier tube has me puzzled. I ordered a new GZ34 off EB and got a new 5AR4. After searching Google it looks like they are interchangeable. Are they? I checked the item descript again and it does say "5AR4\GZ34" so I guess I got what I ordered. It's Shuguang if that means anything. I also Googled them and found good and bad comments just like all the others -except Mullard. The only complaint I found with Mullard was the price. Yeouch!

The slight progress feels good and I'm having fun bringing this old amp back to life. Should have done this a long time ago.

Thanks!
Randy


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jul 07, 2013 8:18 pm
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Yes, the GZ34 and 5AR4 are directly equivalent to one another. They share a single entry in the RCA Receiving Tube Manual (all editions), which for many is the tube Bible.

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Wed Jul 10, 2013 9:09 pm
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Not there yet but she's improving.

In addition to the new rectifier tube I have replaced all paper caps plus 3 resistors and 1 volume control. The vol pot was grounded well but had noise that would clear up when I touched the shaft which led me to believe the problem was internal. I used Deoxit D5S6 to clean the sockets, pots and jacks. I'm not sure how much it helped the amp but it made me feel a lot better.

Tremolo works well when set deep but not so well with a shallow setting - but it works. Reverb works but is short and shallow and basically sounds like crap. The hissing is still there even with the volume turned to 0 but I can tolerate it if needed. Gone are the intermittent pops and cracks in the background!

Here come the questions..... :)

I've got 2 ceramic disc caps that are microphonic when poked with a stick - I hear the tapping through the speakers. I also hear it slightly when lightly tapping the 12AX7. I'm going to change the tubes anyway but is any microphonic response from a tube or cap considered acceptable, or does it mean they are about to turn tango uniform on me? They may last for years but if they are affecting the tonal quality of the amp then I will replace them now. I really want to get that Fender sound back.

I've got a new 4AB3C1B tank on the way but that's it for the cheap parts, then it starts getting more expensive. Get new tubes, then find a decent set of speakers to replace the 16 ohm Celestion GM12 and 4 ohm Pyle mystery speaker. The amp doesn't sound like a Fender right now and I hope my expectation of the replacements is not unrealistic, but I'm sure hoping to get that old tone back. I'll be several hundred deep if I don't.

Since I'm not close to a source where I can test or listen to various models I will likely go with some new greenbacks or something similar since I know those are capable of producing the Fender sound. I tried YouTube, but clips with different amps, guitars, settings, microphones, bit rates etc. is not a very accurate method of selecting speakers.

If or when I get the Fender tone back I'll tackle the amp cabinet and replace the tolex and grill cloth. It's not a truly original 65 anymore so I may as well plan for a face lift if everything else starts working and sounding the way it should.

That's it for this week. I'll get the 3 prong power cable added and remove the death cap later this week.

You folks have been a tremendous help and I wouldn't have gotten this far without it.. Please know it's greatly appreciated.

Randy


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Wed Jul 10, 2013 10:14 pm
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I wouldn't bet the ranch on those Greenbacks delivering any sort of vintage Fender tone. A more appropriate speaker would be Weber's 12F150 (no doping) or some vintage Jensen C12N's if you can find them.

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Thu Jul 11, 2013 5:02 pm
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Retroverbial wrote:
I wouldn't bet the ranch on those Greenbacks delivering any sort of vintage Fender tone. A more appropriate speaker would be Weber's 12F150 (no doping) or some vintage Jensen C12N's if you can find them.

Arjay

My head wasn't screwed pm straight. C12N is what I was thinking but wrote something else. Was looking at Weber at musiciansfriend but they no longer have them listed.


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Thu Jul 11, 2013 5:20 pm
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" I've got 2 ceramic disc caps that are microphonic when poked with a stick - I hear the tapping through the speakers. I also hear it slightly when lightly tapping the 12AX7. "

This is the bad thing about ceramic disc caps, they can be noisy. A little silicon sealer glue or a glue gun onto the body of the cap, tacking it to the breadboard or other cap (if it/s those 0.02/0.01/0.01 caps in a row) --- can sometimes cut down the noise.

Most all gain stage tubes will make some level of noise, if tapped. As long as it isn't ringing, you are prolly ok. Sometimes a totally noise-free tube is kinda dead sounding.

Good luck with all that!


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Thu Jul 11, 2013 9:06 pm
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Thanks BMW-

Looking at the schematic I believe it's the 01 and 047 at opposite ends. I'm not all that concerned but I will see if I can pad it with some hot glue or silicone.

Question about tubes: Those 7025's are mucho expensive compared to the 12AX7. IYO, how would it change the tone if I used 12AX7 tubes, or is that considered a bad idea?

Thanks


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Thu Jul 11, 2013 10:13 pm
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The military-developed 7025 dual-triode is similar in most respects to the 12AX7. However, it's designed and engineered to have a better signal-to-noise ratio for use in high-end audio and commercial-broadcast equipment. Leo chose this tube to keep his amps quiet at idle. Tone differences between the two tubes may or may not exist but the 7025 will provide an improved noise floor. The enhanced 12AX7A is the direct consumer equivalent to the 7025.

Arjay

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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Thu Jul 18, 2013 9:39 pm
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What an amazing difference a little TLC can make!

After replacing all the filter caps and cleaning up the pots and sockets with some Deoxit the amp still had some noise right off standby but I decided I could live with that, then as I was sliding the amp back in the cabinet I noticed the screen mesh up top and realized it must have been designed that way to shield the chassis. Sure enough I buttoned it all up and hit the switch and it's almost as quite as my SS red knob Princeton. I don't know how much noise is normal for these old amps but I'm happy with it.

So far I've replace all the paper caps, a couple of resistors, one volume pot on the trem side, replaced the reverb tank (the old one was not OEM Fender) used Deoxit on anything that moved or had a socket, then ditched death cap and 2 prong AC plug for a 3 prong with ground. It's never sounded better and I wish I had done this years ago.

Now I'm on the hunt for some decent speakers that won't break the bank and a bias probe.

One more question if you don't mind: I've read some tips on how to lower the volume for home use while bringing out the grit a little early by removing the V1 tube and changing AX7's for AT7 or AY7's etc. Are these changes harmful to the amp?

You guys have been a huge help and I appreciate all of it.

Randy


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Thu Jul 18, 2013 10:02 pm
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" One more question if you don't mind: I've read some tips on how to lower the volume for home. "

Edit: Oops! I read lower the voltage not volume. :oops:

Subbing a 12AT7, 5751, 12AY7 into a 12AX7 will not harm your amp. However, the actual change in volume may not be as great as you first imagine. This is because the overall gain in any section is dependent on several factors, not just the tube type. And the nature of "loudness." To decrease the apparent loudness (to our ears) by a factor of two --- you need to decrease the wattage by a factor of ten.

Even, pulling pairs of output tubes (in a quad arrangement) or subbing four 6V6GT into a Twin Reverb, may not decrease the volume all that much.

The four 10-inch speakers have as much to do with overall volume as any tube or tranny in the amp. I run my SR into a PR cab (one ten inch) every now and then. The change in impedance (8-ohm versus 2-ohm) and the decrease in radiating surface area decreases the overall volume as effectively as any electrical modifications to the amp, IME. I wouldn't recommend this as a permanent solution.

Best to find a nice VC or PR -- for "porch weasel" use (as Arjay would say). Then, you get all the nice OD tones of the 6V6GT at sane volume levels.


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jul 21, 2013 8:40 pm
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BMW2002Ti wrote:
" One more question if you don't mind: I've read some tips on how to lower the volume for home. "

Edit: Oops! I read lower the voltage not volume. :oops:


Now it makes sense.

Can you tell me if I can bias the amp with one of those one hole wonders or do I need use a dual bias probe?

Thanks,
Randy


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Post subject: Re: 65 Pro Reverb with weak reverb
Posted: Sun Jul 21, 2013 10:50 pm
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Randy, you can use the single socket adapter bias probe for any amp that has a BIAS POT. Like the AB763 Super Reverb. Just move between the two sockets and adjust the one pot to best get both tubes into a 10-15% range of the target goal. As usual, check for red plating and overheating.

The later circuits like the AB568, AA1069, & AA270, & AA1069 utilize this pot for BALANCE adjustment between the two 6L6GC's. And cannot be used to adjust the overall bias placed on the two 6L6GC's.

Be sure your "bias pot" is in a circuit similar to the AB763. I usually buy "matched" 6L6GC's. At least, the tubes stay within reasonable range for awhile --- all tube age differently with use.

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

The advantage with the BALANCE POT is you can adjust the amp to help balance out un-matched output tubes. But, due to other features of the AB763 circuit versus later ones -- DO NOT mod the AB763 to later ones. For re-sale reasons.

Good luck!


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