J Luth 7/10/2018 7:14 PM
1964 No Logo Deluxe Reverb Strange Issue
Strange issue after the amp is turned on, warmed up and the volume set to just about any level. If a string or a chord is struck or strummed the output level sounds a bit weak. If done again but this time the strings are struck or strummed harder the output level jumps up and stays there. Not talking about the volume going up because the strings are being hit harder, the actual output volume of the amp goes up. If the amp is shut down for a while and turned back on it does the same thing.

If I remember correctly this amp has never been touched and is in great condition, everything inside is original and in good condition. I haven't been inside it in a while. It is here again but I haven't opened it up. The owner is not sure if he wants it gone through and recapped and anything else done other than the weird volume issue. Due to the condition of the amp, he does not use it to play out, just for practice.
 
Randall 7/10/2018 7:52 PM
I would feed the amp a signal from a generator or ipod or phone, just not a guitar because you will need both hands. Turn the amp on and while it is cold probe around with a chopstick to see if moving, tapping, flexing or putting pressure on something makes it get louder suddenly. Include the speaker wires if they are not soldered. Check the speaker jack and plug connection. I had a Victoria 410 Bassman do this once, it turned out the speaker plug was faulty. Rock all tubes to see if there is a dodgy or oxidized socket. Check input jacks, does it do it on both, does it do it on both the Normal and the Reverb channels?
 
galaxiex 7/10/2018 8:42 PM
Yep, it sounds like a dirty, weak, corroded connection somewhere.
 
J Luth 7/11/2018 3:52 PM
Thanks for the suggestion, I found it. I tapped around in the amp with no change until I tapped the volume pot connections. Re-soldered the connections, no change. Hooked it up to the scope and got a very bad looking sine wave. When I would play around with the volume control the sine wave would change. It would get cleaner and would occasional increase. There was a 47pf cap across the volume pot. tapping it made a slight difference but not every time. I pulled it out and it cleaned up the sine wave some. The amp does need to be recapped, they are all way over value. On to the next question. Not going to get a good looking sine wave until it's recapped.
 
J Luth 7/11/2018 3:59 PM
I spoke to the owner and he has decided to go with recapping the amp. All of the 25/25 are way out, up to 140uf and bulging, most of the 16uf's are out a bit but are stating to bulge and leak. So they all have to go.

He asked me a question that I am not sure of the correct answer.

The main filter caps are 16uf 450v he asked if changing them to 22uf would change the sound of the amp? He was told by someone that they should be increased to 22uf. I told him I can do it either way he wants it.

Any opinion's on that?
 
The Dude 7/11/2018 4:19 PM
I haven't heard of caps being that far out of tolerance and higher UF. Are you certain of your testing methods? Try a known good/new cap with the same test. It's not uncommon for older caps to have higher than labeled values as tolerances were not as "good" in the day, but that seems extreme.

On the filter caps, you won't notice any difference going from 16UF to 22UF and 22 is a standard value. If you do notice a difference, it's not because of the difference in value, it's more likely because the old caps are shot.
 
Enzo 7/11/2018 4:24 PM
The old days saw caps with typical tolerance of +80/-20%. SO a typical 16uf cap can measure as high as 28uf and still be within spec. There is nothing with a critical value in a guitar amp.

I recommend 22uf caps because they are a standard value, and available anywhere. 16uf is not a standard value. It might have been 50 years ago, but then I was just a college boy, and gas was cheap. So not only will it be easier and cheaper to go with 22uf, it won't even be outside the original specs. Modern caps are much closer tolerance.

Will it change the sound of the amp? Probably, but not because of the value of those couple caps. it will change because it will now have new fresh caps. He likes the way the amp sounds with bloated, off-value, worn out caps. Nice fresh new caps are going to make the amp sound different. Will it make a Deluxe sound like a MArshall or something? No not at all. But it will sound more like a new Deluxe rather than an old tired one.
 
Enzo 7/11/2018 4:26 PM
Leaky caps can take longer to charge and fool some meters into thinking higher capacitance.
 
J M Fahey 7/11/2018 4:27 PM
If they are being measured in circuit, the parallel 1k5 cathode resistor may be misinterpreted by meter as a far higher capacitance.

Unsolder at least one leg for measuring.
 
Helmholtz 7/11/2018 4:33 PM
Quote Originally Posted by J Luth View Post
I spoke to the owner and he has decided to go with recapping the amp. All of the 25/25 are way out, up to 140uf and bulging, most of the 16uf's are out a bit but are stating to bulge and leak. So they all have to go.

He asked me a question that I am not sure of the correct answer.

The main filter caps are 16uf 450v he asked if changing them to 22uf would change the sound of the amp? He was told by someone that they should be increased to 22uf. I told him I can do it either way he wants it.

Any opinion's on that?
I cannot help but mention that e-caps never go up in value by age, in fact capacitance reduces over time because the electrolyte dries out. Your measurement values seem to be the result of increased leakage conductance and a crude measuring principle/meter.

Increasing the filter caps to 22 may slightly reduce the amp's responsiveness in favor of tighter lows.
 
Enzo 7/11/2018 4:35 PM
Increasing to 22 will slightly reduce the amp's responsiveness in favor of tighter lows.
Assuming the original 16uf caps were actually 16uf to start with.
 
Leo_Gnardo 7/11/2018 4:37 PM
Quote Originally Posted by J Luth View Post
So they all have to go.
Best plan yet. As for 22 uF "sounding different" as hi voltage filters, let's put it this way. Some people imagine they can hear a difference, and get all bent out of shape if the exact replacement part isn't installed. Those people, they're the reason the "Princess and the Pea" fable was written. Use 22's, and rest your mind, you've done the right thing.
 
Helmholtz 7/11/2018 5:04 PM
If they are being measured in circuit, the parallel 1k5 cathode resistor may be misinterpreted by meter as a far higher impedance.
I guess you mean lower impedance.
 
J M Fahey 7/11/2018 6:27 PM
Quote Originally Posted by Helmholtz View Post
I guess you mean lower impedance.
Sorry, brain fart, I meant higher *capacitance* , which is what we are talking about.
Thanks for the eagle eye.
 
The Dude 7/11/2018 7:06 PM
I gave you a thumbs up anyway. I knew what you meant.
 
Chuck H 7/11/2018 9:15 PM
Quote Originally Posted by Enzo View Post
The old days saw caps with typical tolerance of +80/-20%. SO a typical 16uf cap can measure as high as 28uf and still be within spec. There is nothing with a critical value in a guitar amp.

I recommend 22uf caps because they are a standard value, and available anywhere. 16uf is not a standard value. It might have been 50 years ago, but then I was just a college boy, and gas was cheap. So not only will it be easier and cheaper to go with 22uf, it won't even be outside the original specs. Modern caps are much closer tolerance.

Will it change the sound of the amp? Probably, but not because of the value of those couple caps. it will change because it will now have new fresh caps. He likes the way the amp sounds with bloated, off-value, worn out caps. Nice fresh new caps are going to make the amp sound different. Will it make a Deluxe sound like a MArshall or something? No not at all. But it will sound more like a new Deluxe rather than an old tired one.
+1
In fact, that +/- was typically on the + side. So those old 16uf caps were commonly 20+uf. I always go with 22uf for it's availability. Which comes with selection options so your not stuck using some boutiquy thing that may be mediocre, but is labeled at 16uf to indicate it's "specialness". 22uf all day
 
J Luth 7/11/2018 11:21 PM
I'll double check the 25/25. The reading was way off in circuit but the final check was with them out of circuit. It could be my eye's as I posted about them in a in a previous thread.
 
J Luth 7/11/2018 11:22 PM
It's his choice. Antique has bot 16uf and 22uf listed. Yes the 22's are a bit cheaper.
 
J Luth 7/11/2018 11:25 PM
Measured both in and out of circuit. Going to check again tomorrow just to see could have been my eye's. They do play tricks on me from time to time. Sometimes it's a PITB. The are going to be replaced anyway.
 
J Luth 7/11/2018 11:26 PM
Kind of like the blind listening test.
 
Helmholtz 7/12/2018 6:15 AM
In fact, that +/- was typically on the + side. So those old 16uf caps were commonly 20+uf. I always go with 22uf for it's availability. Which comes with selection options so your not stuck using some boutiquy thing that may be mediocre, but is labeled at 16uf to indicate it's "specialness". 22uf all day
Have you ever seen one of these old caps that measured more than 20% above rated value? Me not.
 
Chuck H 7/12/2018 6:37 AM
Quote Originally Posted by Helmholtz View Post
Have you ever seen one of these old caps that measured more than 20% above rated value? Me not.
Well, ok... I've seen an 8uf that measured 10. So that's 20% (though not above). I can't remember about other's as specifically except that they always seemed to be AT LEAST the posted uf value and usually higher by a tad. But there were also old caps I never measured because they were getting replaced anyway. So I can't say about any decrease with age. It's not like we can measure them the way they were I also have a limited ability to measure value because I don't have a proper bench tool. I just use my 87 which has a limit of 4.7uf. I put another cap in series with the one I'm measuring and math the result.
 
Helmholtz 7/12/2018 7:07 AM
Quote Originally Posted by Chuck H View Post
Well, ok... I've seen an 8uf that measured 10. So that's 20% (though not above). I can't remember about other's as specifically except that they always seemed to be AT LEAST the posted uf value and usually higher by a tad. But there were also old caps I never measured because they were getting replaced anyway. So I can't say about any decrease with age. It's not like we can measure them the way they were I also have a limited ability to measure value because I don't have a proper bench tool. I just use my 87 which has a limit of 4.7uf. I put another cap in series with the one I'm measuring and math the result.
Well I certainly know about decrease with age. In many applications the lifetime of the equipment is determined/limited by the filter cap. We did real lifetime testing (i.e running hundreds of SMPS over years at max. ambient temperature) and checked samples for C and ESR at intervals. The end-of life criterion was C down to 60% of rated value.
 
Chuck H 7/12/2018 7:35 AM
Oh, I wasn't saying it doesn't happen. I was noting that those older caps I've bothered to measure seem to be as much or greater than their rated value. If caps lose value with age then I would expect they were higher when new. I shot high.
 
Helmholtz 7/12/2018 8:17 AM
If caps lose value with age then I would expect they were higher when new.
They surely were. But the results are rather individual. C decrease is influenced by operating hours, temperature and the quality of the seal.
The caps I had to replace (because of high ESR and leakage current - I usually just go by the too low Q-value) were often down by > 20%.

I was just curious if someone had actually seen old filter caps (still) measuring 50% or 80% above rated.

My oldest e-cap data book (Siemens,1961) specifies +50%/-20% for HV types and even +100%/-20% for LV types.
 
J M Fahey 7/12/2018 9:31 AM
Quote Originally Posted by Helmholtz View Post
I was just curious if someone had actually seen old filter caps (still) measuring 50% or 80% above rated.
50/60 years later? ... that would be very unlikely.

That said, **maybe** we have "seen" them, but how would we know it?

People normally do not measure every cap they see, just for fun, unless them being suspect.

Except maybe a guy with a brand new Capacitance meter (or a Network Analyzer for that matter ) who to play with his toy measures *everything* around, even his chocolate chip cookies.
 
dstrat 7/12/2018 9:57 AM
Quote Originally Posted by J M Fahey View Post
even his chocolate chip cookies.
I need some 500v chocolate chips cookies!
 
Helmholtz 7/12/2018 10:17 AM
Except maybe a guy with a brand new Capacitance meter (or a Network Analyzer for that matter ) who to play with his toy measures *everything* around, even his chocolate chip cookies.
Well, sometimes I am a little like that
At least I always make sure that I understand what I am doing and how the "analyzer" works.
The measuring experience thus gained often has helped me in my job as R&D manager. We physicists are a little different (strange?), you know: Curious and extremely eager for knowledge.
 
Enzo 7/12/2018 3:19 PM
Well that is a major difference in approach between technicians and engineers. Engineers tend more toward the theoretical, while technicians dwell on the practical. When I decide a cap needs to be changed, I change it, and don't bother spending a lot of time analyzing the bad part. I already know it is bad.

As a technician, I am also curious and eager for knowledge. But it is a different sort of knowledge. Just as a symphony violinist has different things on his mind than does a bluegrass fiddler. Maybe the bluegrass guy can't read sheets, but the symphony guy can't jam and ad lib. Both are highly skilled.

I have decades of experience handling tools, disassembling and assembling stuff. The engineer has decades of experience running sims and other software. The engineer might toss up a breadboard now and then, just as the technician might look up a data sheet now and then.

When I was a kid, electronics was my hobby, and I was all into load lines, and curves, and formulae. As a technician, I have not had the need to draw a load line in 40 years.

The engineer might hand a schematic to a technician and say "here, put this together for me." The technician might hand a circuit to an engineer, and say "This goes into oscillation if the power supply drops below 14v."

An engineer might order 11.2 ohm resistors (A particular Yorkville/Traynor power amp comes to mind). A technician knows that if his 220k plate resistors have drifted to 290k, that still isn't the reason the amp makes no sound.
 
Helmholtz 7/12/2018 4:40 PM
Quote Originally Posted by Enzo View Post
Well that is a major difference in approach between technicians and engineers. Engineers tend more toward the theoretical, while technicians dwell on the practical. When I decide a cap needs to be changed, I change it, and don't bother spending a lot of time analyzing the bad part. I already know it is bad.

As a technician, I am also curious and eager for knowledge. But it is a different sort of knowledge. Just as a symphony violinist has different things on his mind than does a bluegrass fiddler. Maybe the bluegrass guy can't read sheets, but the symphony guy can't jam and ad lib. Both are highly skilled.

I have decades of experience handling tools, disassembling and assembling stuff. The engineer has decades of experience running sims and other software. The engineer might toss up a breadboard now and then, just as the technician might look up a data sheet now and then.

When I was a kid, electronics was my hobby, and I was all into load lines, and curves, and formulae. As a technician, I have not had the need to draw a load line in 40 years.

The engineer might hand a schematic to a technician and say "here, put this together for me." The technician might hand a circuit to an engineer, and say "This goes into oscillation if the power supply drops below 14v."

An engineer might order 11.2 ohm resistors (A particular Yorkville/Traynor power amp comes to mind). A technician knows that if his 220k plate resistors have drifted to 290k, that still isn't the reason the amp makes no sound.
I leave it to engineers to comment

My engineers did very well with practical as well as theoretical stuff. One technician with 10 engineers worked perfectly.
And my practical experience and skills aren't too bad either.
 
Enzo 7/12/2018 5:50 PM
My engineers did very well with practical as well as theoretical stuff. One technician with 10 engineers worked perfectly.
And my practical experience and skills aren't too bad either.
yes. of course overlap. it depends on what the job is. Are your 10 engineers and one technician responsible for designing things or are they responsible for maintenance and repair of things? I think in my pro audio repair facility that ration would be reversed. Just saying one is not superior to the other, just doing different jobs.


In one life I serviced juke boxes, and trained techs how to do it. Seeberg jukes have a mechanism - the mechanical part that scans back and forth and picks up the record and plays it - that is a mechanical marvel. A motor on a frame that drives cams and clutches and gears. Seven moving parts just to make a tiny brush quickly sweep up and down as the tone arm goes by to brush any lint off the stylus. Tone arm assembly slid side to side to get on the proper A or B side of a record. There were stacks of blade switches, oiling points, adjustment screws. I am truly impressed with this complex machine. Unfortunately whoever designed it never worked on them. Instead of an access door in the rear of the juke so you could put it in front of your nose, they made the whole mech and magazine slide forward - after you removed the front of the jukebox - and then it was hinged so it could be tilted towards you to expose the rear. And there was even a brace and chain to allow it to be suspended in that position.
 
Helmholtz 7/13/2018 9:00 AM
Just saying one is not superior to the other, just doing different jobs.
Agree and would like to add...and sometimes doing the same job with a different approach. What counts are efficiency and results. I don't like this technicians vs. engineers or engineers vs. physicists stuff. But I admit that often different "languages" and methods are used. I try to stay away from generalization and prejudice.

I hope you are not telling me that this forum is for technicians only?

That said, I have the highest respect for your experience and analyzing skills as well as your patience with posters.
And I would not have interfered in your response above if I would have seen it before my posting as "too many cooks spoil the broth" and I don't think you need my help.
 
Enzo 7/13/2018 4:21 PM
I hope you are not telling me that this forum is for technicians only?

No no no no...

I never intended it to be an us versus them thing, I was just expounding on that aspect of electronics. I was the technical rep for an amusement product many years ago. The engineers came over from the UK to show me the product and how it worked. It was then up to me to support the product, train others in its use, and in fact even tweak the circuits to do extra things we wanted. I was the monkey crawling under the thing. They were the guys who came up with the design in the first place.

I love to see new cooks in the broth. I like to see people put the same idea into words as I did, but using totally different words. Likewise I often restate someone's point in a different manner. The more ways something is presented, the more likely it will reach someone trying to understand.

So many novice techs are afraid of the technology involved, and I like to present things in a casual dis-arming manner to help them relax and look at the circuits. And as useful as a network analyzer might be, I want kids to know you don't have to have one to work on your old Fender.
 
Tone Meister 7/14/2018 2:28 PM
Quote Originally Posted by Enzo View Post
... As useful as a network analyzer might be, I want kids to know you don't have to have one to work on your old Fender.
Damn, I'm glad someone finally said it. Whew!
 
Helmholtz 7/14/2018 3:07 PM
Quote Originally Posted by Tone Meister View Post
Damn, I'm glad someone finally said it. Whew!
Who claimed the contrary?
You don't need a scope for simple repairs. But it helps to understand what's happening. Things change when you start to design your own stuff. Measuring is the key to understanding.
Same with simulations.
Why not use an analyzer when it's available and may give some clue?
 
Enzo 7/14/2018 4:25 PM
cerrem more or less did.

Nothing wrong with using everything at your disposal. The OP was concerned that his amp lost level.
 
Helmholtz 7/14/2018 4:55 PM
The OP was concerned that his amp lost level.
Yep, and he hasn't reported back since post #19, keeping us idling.

cerrem more or less did.
...and I proved him wrong without using an expensive analyzer.
 
Chuck H 7/14/2018 5:11 PM
Quote Originally Posted by Helmholtz View Post
Yep, and he didn't report back since post #19, keeping us idling.
I tend to do that here sometimes. The info Luth needed was given and he's right in the middle of a project and on to some new issue now... Too busy to post until he has his new questions sorted out It's what we do
 
J Luth 7/17/2018 7:20 PM
OK, back at it. I have not been ignoring this thread, I have been very busy with other things that came up and gone for the past weekend.

Also WHOOPSY, in the post that I typed way out up to 140UF, that was supposed to be 40UF. Sorry bout that. Yeah it's a cheap meter but it was my fault on the post. I had it checked by someone today with a better meter and he got 35UF.

The owner has chosen to recap the amp.

One more question.

On pin 1 of V5 the schematic and layout show +270V, could that be a typo? The actual reading there is around 414 or there abouts not near the amp right now going on memory. All resistors check OK. The wire feeding pin 1 is connected to a 200K resistor which the other side of the resistor is connected to the junction of the 100K and 10m which is feed directly off the filter cap. Wouldn't the voltage on pin 1 be a lot higher than 270V?
 
Chuck H 7/17/2018 8:18 PM
That would be the trem tube (I think, there are no V#'s on 1964 Fender schematics ). Is the tremolo working? Clearly something is hinky with the ground for the cathodes of that tube because the high plate voltage would be a symptom of the tube not drawing any current. Perhaps this could be the case for other tubes or circuits as well.?. Any other grossly high voltages? Panel controls that either don't work or seem to work incorrectly?
 
g1 7/18/2018 11:53 AM
Is that with the trem off that you get the 400V at the plate? Voltages shown are with oscillator running. I wouldn't worry unless there is a trem fault.
 
Chuck H 7/18/2018 8:04 PM
Quote Originally Posted by g1 View Post
Is that with the trem off that you get the 400V at the plate? Voltages shown are with oscillator running. I wouldn't worry unless there is a trem fault.
I thought of that too. Then I thought it shouldn't much matter since it's the signal path that interrupted on the oscillator and nothing about it's idle current. I still thought 414V was high. High as in no current at all.?.
 
J Luth 7/18/2018 9:11 PM
Yes it's the trem tube. Yes the trem works and works well. That was the only one that was out a lot, I'll double check the voltages on the other tubes again to make sure. All controls are working. The amp will get a full test tomorrow. I'll also take a look at the grounds.
 
J Luth 7/18/2018 9:14 PM
The reading would have been with the trem off, nothing connected to the RCA.
 
J Luth 7/19/2018 10:23 AM
Chuck,

Rechecked everything today and the trem tube was the only one showing high voltage. I checked a few things and found that one of the cathode ground wires had a bad solder connection, it pulled right off the brass ground plate. Fixed that and retested with the trem on and all is OK.
 
g1 7/19/2018 11:59 AM
I'm not sure if we're still talking about the high voltage at the plate of the trem osciallator or not.
I hope you are not saying that after you corrected the ground connection it changed that plate voltage when trem off?
I'm attaching the schem. from the '65 DRRI as is shows more voltages. With trem off, the voltage at the cathode is zero. With zero current through the tube, I expect the plate voltage to rise to the voltage at supply node 'Z', around 400V. On a real AB763 schematic, that node is shown as 415VDC.
 
J Luth 7/19/2018 2:57 PM
g1

Yes I am still referring to the trem.

No the plate voltage did not change much if any. The voltage reading is correct with the trem on.
I did not take a voltage reading with the trem on in the first post. Didn't know that it had to be on.
DOH live and learn I guess.

I should have stated in the last post that states it's OK, that it was checked with the term on.

It reads around 412v with the trem off and around 270v with the trem on, Going from memory right now

But at least I did find a bad solder connection on the ground.

Thanks for the Service Manual