1968 Fender Deluxe Reverb - any help/insight on an issue?

mkstewartesq

mkstewartesq

Well-known member
(If this should be in Troubleshooting", my apologies - but it isn't a pedal problem so I was unsure).

So, before I run off to a dedicated amp forum where I don’t know anyone, I thought I would first ask this question of all the knowledgeable people here I trust:

I have a vintage 1968 Fender Deluxe Reverb (early silverface with drip edge), AB763 circuit. I’ve owned it since 1984 but not played it in a while so I had a well-known local amp tech go over it and get it back up to speed. But I’m guessing he didn’t test it by playing loudly.

At anything above about 3.5 - 4 on the volume, you get a deep rumble on the bass notes - it swells and then fades, and almost has a phasey quality. It will do this sooner if you use a guitar with higher output pickups (or with single coils wired in series) or even if you roll the tone knob off so the guitar is mainly pushing bass frequencies. Driving it with a compressor has the same effect. Anything above that volume is just fuzz city and unusable.

Both channels (normal and vibrato) exhibit the same behavior. Treble at 6, bass at 3. I tested with an external speaker and the external speaker reproduced the same sound, so my internal speaker doesn’t appear to be the culprit.

I found this video online which is a pretty good representation of the sound – but in all the threads I’ve searched, no one has offered a good solution.

Any thoughts or suggestions from the brain trust here?

As always, thanks.

Mike
 
mkstewartesq said:
(If this should be in Troubleshooting", my apologies - but it isn't a pedal problem so I was unsure).

So, before I run off to a dedicated amp forum where I don’t know anyone, I thought I would first ask this question of all the knowledgeable people here I trust:

I have a vintage 1968 Fender Deluxe Reverb (early silverface with drip edge), AB763 circuit. I’ve owned it since 1984 but not played it in a while so I had a well-known local amp tech go over it and get it back up to speed. But I’m guessing he didn’t test it by playing loudly.

At anything above about 3.5 - 4 on the volume, you get a deep rumble on the bass notes - it swells and then fades, and almost has a phasey quality. It will do this sooner if you use a guitar with higher output pickups (or with single coils wired in series) or even if you roll the tone knob off so the guitar is mainly pushing bass frequencies. Driving it with a compressor has the same effect. Anything above that volume is just fuzz city and unusable.

Both channels (normal and vibrato) exhibit the same behavior. Treble at 6, bass at 3. I tested with an external speaker and the external speaker reproduced the same sound, so my internal speaker doesn’t appear to be the culprit.

I found this video online which is a pretty good representation of the sound – but in all the threads I’ve searched, no one has offered a good solution.

Any thoughts or suggestions from the brain trust here?

As always, thanks.

Mike
Click to expand...
I'd try a different set of tubes if possible.
 

Distortion

www.geofex.com

I don't know your amp tech but I can make some rough assumptions that voltages were probably checked so you're not likely looking at resistor(s) or power tube bias. I also don't think they'd miss anything by not turning it up ... travel is hard on amps so even the car ride back home could be enough to junk your tubes.

amp techs don't do cap jobs without getting cap job prices so I imagine this is the root cause seeing as you didn't mention a cap job in your OP

BUT

I wouldn't cap job or buy a full set of tubes without first doing a little bit of testing.

I'd want one (yes, one) known good 12AX7 that I could swap in place of the preamp tubes (one at a time) moving from input to phase inverter. I'd take good notes on any differences in sound if the problem isn't resolved because we've introduced a variable so if we start getting different results but no resolution we can infer that is the section of circuit we need to hone in on. If you have spare power tube(s), I'd swap those as well just to see.

If you got lucky and a single tube swap fixed it, go ahead and replace all the tubes.
If not, do the cap job and retest. The 80s were a long time ago.
 
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Guardians of the analog said:
Sounds like it could be a bad cap. Do you have a list of what the tech "fixed" ?
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He replaced one cap, although for the life of me I can’t remember exactly which one/what its purpose was (he’s a long drive and only open on the weekdays, so I only had a very brief time to pick up the amp and get back to work). But should you enjoy looking at pictures of caps (since I’m 100% positive it would mean more to you than me), this is the cap he took out.

EDIT - I just remembered that he said he had to replace the cap because the vibrato channel was ticking when the vibrato was engaged. So that’s what it related to.

Thanks for taking the time, sincerely.

IMG_3577.jpeg
 
ICTRock said:

Distortion

www.geofex.com

I don't know your amp tech but I can make some rough assumptions that voltages were probably checked so you're not likely looking at resistor(s) or power tube bias. I also don't think they'd miss anything by not turning it up ... travel is hard on amps so even the car ride back home could be enough to junk your tubes.

amp techs don't do cap jobs without getting cap job prices so I imagine this is the root cause seeing as you didn't mention a cap job in your OP

BUT

I wouldn't cap job or buy a full set of tubes without first doing a little bit of testing.

I'd want one (yes, one) known good 12AX7 that I could swap in place of the preamp tubes (one at a time) moving from input to phase inverter. I'd take good notes on any differences in sound if the problem isn't resolved because we've introduced a variable so if we start getting different results but no resolution we can infer that is the section of circuit we need to hone in on. If you have spare power tube(s), I'd swap those as well just to see.

If you got lucky and a single tube swap fixed it, go ahead and replace all the tubes.
If not, do the cap job and retest. The 80s were a long time ago.
Click to expand...

This is an excellent suggestion regarding testing a single tube – I’ll need to figure out where to get one (when I was growing up, back in the Stone Age, they were much more easy to get locally).

And, yes, I agree with you that I think I can trust the tech with a lot of the basic testing. He’s actually really well known in this area as the best and pretty much the only guy that the high-end stores around here recommend for repair – his name is Jeff Bakos and apparently he also does a lot of work for some fairly significant artists.

And it’s a good point about additional factors like travel possibly having an effect. He mentioned to me that he stress tested the amp by leaving it on for several hours after he did his work (basically checking that everything was functional, replacing the power cable with a three prong, replacing a bad cap) but when I got it home after a long day in the car, it seems like the optocoupler for the vibrato had finally died after 16 years (he swore that it was working during his stress testing) so that could’ve been given its final death below on the trip home. I trust him that it was working when he had it because, as mentioned above, he specifically replaced the cap to get rid of ticking when the vibrato was engaged.
 
jimilee said:
Meh, I’d call him back and tell him it’s not right.
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I may end up doing that, but I'm looking to troubleshoot what I can first because it is an ungodly trek to get down to him.

I realized I do have some good 12AX7s in a barely used Bues Junior I bought about a year ago. so I can at least try that. Looking at the docs for the AB763, it looks like only one preamp tube serves both the normal and the vibrato channel (the phase inverter tube) so that will be my first slot to try, since I hear the odd effect in both channels.

M
 
ok now I see that he did one capacitor and that one capacitor is from 68 ... so you need a cap job. not some of them, all of them (electrolytics like the one pictured). I'd do tubes at the same time but I don't shop with other people's wallets.
 
I'm with Jimi, only because any repairs I do that aren't up to snuff, people call me out on. Luckily that doesn't happen often but I've had instances where it was an issue I totally missed or didn't think I had to test for. You spent good money I suspect and the tech needs to make it right.

Granted it may cost you more if it's something he missed and is a legitimate charge but then again I tend to eat labor costs if it's something I miss. I do this more as a hobby than a living so my mileage varies. If I didn't nail it the first time I consider it MY problem.

As a tech I really don't like to look stupid and if a customer isn't totally happy, I look stupid.
 
I’d try a new rectifier, since the caps were specifically looked at. I’m suggesting this because I went through a few weeks of having an amp play fine with my Strat or low wind humbucker guitars, but it would begin to fart out with my baritone. My first thought was the power tubes, but the bias was great, and my back up pair (still new), when biased, did the same thing. A new rectifier tube did the trick. And I'll plug the brand, since it was new to me—Psvane. When this did the trick, I raided my hifi tube stash, and subbed in a NOS GE and Amperex rectifiers, out of curiosity; the Psvane was right there with them, at a good price.

I don’t think a preamp tube would exhibit that type of choking sound.
 
Guys –

Thank you everyone for the advice. Just wanted to update that I actually don’t think that it is the amp that is the problem (or at least not the main problem).

When I got the amp back from the shop this last time, I hooked it up to a new Tone King Ironman II Mini attenuator, which I believe is actually the source of the unpleasant sounds I’m getting. I tested the attenuator on another fender amp I have and got many of the same unpleasant artifacts (including, oddly, making the clean signal sound like it was being run through a fuzz at higher attenuation levels). I’m going to reach out to the company for their thoughts before contacting Sweetwater, just so I know whether I should be asking for a refund or a replacement unit. I hope this is not intended behavior because Tone King attenuators have stellar reviews and I quite like the way it sounds when you are applying only very light and it is not making the sound freak out.

I had already done the preamp tube swap test and it made no difference but I agree with all of the advice given that, with the age of of this amp,, it’s probably getting time for a recap and a full tube replacement. But for my instant problem, I think I need to look at the attenuator, not the amp.

Thanks to all,

M
 
Alan W said:
I’d try a new rectifier, since the caps were specifically looked at. I’m suggesting this because I went through a few weeks of having an amp play fine with my Strat or low wind humbucker guitars, but it would begin to fart out with my baritone. My first thought was the power tubes, but the bias was great, and my back up pair (still new), when biased, did the same thing. A new rectifier tube did the trick. And I'll plug the brand, since it was new to me—Psvane. When this did the trick, I raided my hifi tube stash, and subbed in a NOS GE and Amperex rectifiers, out of curiosity; the Psvane was right there with them, at a good price.

I don’t think a preamp tube would exhibit that type of choking sound.
Click to expand...

Thank you for the tip. Do you need to rebias if you are only replacing the rectifier tube?

M
 
mkstewartesq said:
Guys –

Thank you everyone for the advice. Just wanted to update that I actually don’t think that it is the amp that is the problem (or at least not the main problem).

When I got the amp back from the shop this last time, I hooked it up to a new Tone King Ironman II Mini attenuator, which I believe is actually the source of the unpleasant sounds I’m getting. I tested the attenuator on another fender amp I have and got many of the same unpleasant artifacts (including, oddly, making the clean signal sound like it was being run through a fuzz at higher attenuation levels). I’m going to reach out to the company for their thoughts before contacting Sweetwater, just so I know whether I should be asking for a refund or a replacement unit. I hope this is not intended behavior because Tone King attenuators have stellar reviews and I quite like the way it sounds when you are applying only very light and it is not making the sound freak out.

I had already done the preamp tube swap test and it made no difference but I agree with all of the advice given that, with the age of of this amp,, it’s probably getting time for a recap and a full tube replacement. But for my instant problem, I think I need to look at the attenuator, not the amp.

Thanks to all,

M
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Nice, glad you got it worked out.
 
mkstewartesq said:
Thank you for the tip. Do you need to rebias if you are only replacing the rectifier tube?

M
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I think you should, since the new rectifier is probably running hotter than the old one—although, I don't honestly know. My amp is stupidly easy to bias (check points on the rear face and the adjustment pot is right by the tubes and I added a 5 inch extension to the pot shaft. I'm sure at the time, I noticed a difference, that I am assuming was needing adjustment down, but I just don't remember.
 
I refurb'ed a friend's 1966 DR a few years ago. I replaced ALL of the electrolytic caps. I tested the original tubes and they were all still in-spec. Not too surprising since A) the tubes were all made in the US in the '60s and B) the amp spent most of its life in storage. One of the screen resistors was out of spec, so I replaced both. Also did the Tremolo Click Fix per the factory recommendation. What a sweet amp! I would have liked to buy it from him, but a fair price was out of my range. He ended up getting something like $2.4K on eBay.
 
Chuck D. Bones said:
I refurb'ed a friend's 1966 DR a few years ago. I replaced ALL of the electrolytic caps. I tested the original tubes and they were all still in-spec. Not too surprising since A) the tubes were all made in the US in the '60s and B) the amp spent most of its life in storage. One of the screen resistors was out of spec, so I replaced both. Also did the Tremolo Click Fix per the factory recommendation. What a sweet amp! I would have liked to buy it from him, but a fair price was out of my range. He ended up getting something like $2.4K on eBay.
Click to expand...
Very cool!

@Chuck D. Bones – does the following sound like a symptom of caps going bad to you? I just really have no idea of how failing caps manifests themselves symptom-wise in an amp.

I got a replacement for the Tone King attenuator (it’s a reactive load model), and it exhibits the same sort of rumbling and distortion as the one I already bought when you take the amp up past about 4. So I tried the amp completely unattenuated and, as you bring the volume up, you can hear a very very faint, brief rumbling sound that fades away really quickly- nothing like what comes through the attenuator, but it’s definitely there. The attenuator almost seems to behave like a compressor in that it really amplifies that rumbling/distortion sound and makes it audible even when you would’ve stopped hearing it on an unattenuated amp. Maybe it has something to do with the reactive load nature of the attenuator, maybe not. This is all new to me.

So, long story short – the amp has an issue but the attenuator (functioning properly) really just brings it to the front and makes it much more noticeable. Does that type of sonic artifact in the unattenuated amp sound like a symptom to be addressed with a recap? (To be honest, it’s sometimes sounds a lot like my PPCB Muffler build where I still don’t think I’ve got properly spec’d J201s [EDIT -5485] - rather than cleanly opening and closing the gate, it kind of “fizzles out“ to silence).

Thanks as always,

Mike
 
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