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Deluxe Reverb - "hashy" sound on vibrato channel

Michael Hunter

Silver Supporting Member
Messages
1,910
Despite being perfect in nearly every other way, I've noticed that my '72 DR has this unpleasant "hashy" sound that follows along or under the note when I either crank the amp or boost it with an OD pedal. Get the amp cooking loudly enough and it sounds like a "ripping" or "tearing" sound. It happens exclusively on the Vibrato channel, and there seems to be volume threshold to the problem as well (i.e. lower volume = less of the offending sound, and vice versa). It's far more noticeable on higher frequency pitches than lower frequency ones. The problem disappears entirely when the reverb control is off, so I'm guessing it's a function of something in the reverb circuitry.

I've swapped both V3 and V4 with known good tubes, so the problem doesn't appear to be tube related. The speaker have been swapped as well, and the problem persists. The reverb tank appears to be an Accutronics of recent make; reverb transformer is original. I unfortunately do not own a scope or other diagnostic equipment. Any thoughts as to where I might start looking?
 

Blue Strat

Member
Messages
30,225
Have you swapped V2? V3 is the reverb driver.

Try the amp with V3 pulled. There's a common problem in many of these amps related to the reverb driver circuit...even with reverb turned off.
 

Michael Hunter

Silver Supporting Member
Messages
1,910
I have swapped V2 as well, and currently have a nice Lowrey-branded RCA in that slot. No change. Pulling V3 solves the problem by virtue of getting rid of the reverb. That said, I want reverb! Just don't want the hashy crap that seems to go along with it.

Mike, what's the common problem you're referring to, and does it have an equally common solution?
 

TimmyP

Member
Messages
2,488
Have you checked the tank? It could be that a spring is rubbing.

No, do not try a 16 Ohm speaker.
 

zenas

Member
Messages
8,872
No offense but alot of things can look to be in proper condition in a vintage amp. Tubes and electrolytic caps come to mind.

Got another old Fender Reverb amp you can slide up to this one and try the reverb tank in?

Speaking of electrolytic caps how are they? Are the ones on the board white and say Mallory on them?
 

mark norwine

Member
Messages
17,189
Pulling V3 solves the problem by virtue of getting rid of the reverb. That said, I want reverb! Just don't want the hashy crap that seems to go along with it.

Mike, what's the common problem you're referring to, and does it have an equally common solution?
I'm not Mike, but I stayed in a Holiday Inn Express last night....

This can be cured 100% by placing a 500pF cap from plate to cathode on the reverb driver.
 

andybaylor

Silver Supporting Member
Messages
3,647
No, do not try a 16 Ohm speaker.
Why not? Won't hurt the amp at all.

FWIW- I got that tidbit from a guy named John Phillips. (Very smart guy. His posts were legendary.) He mentioned one of the best Deluxe's he'd heard was using a 16 ohm speaker. (JBL I believe.) Apparently the output of a deluxe reverb is more than 8 ohms?
It's worth a shot. If you have a chance to do it cheaply, do it, and report back!
 

pdf64

Member
Messages
8,056
My preferred solution to the 'V3' issue is a big grid stopper, eg 47k, at the tube socket, or to replace the 1M grid leak with a 470k+470k potential divider.

This acts to help isolate the clipping (of larger signals that occurs at the V3 grid) from the main signal path.

Another problem that can arise in the reverb channel is that as the cathode bypass cap on V4 ages, a degree of positive feedback around V4 is introduced, which increases with the Reverb control setting.
 
Last edited:

Michael Hunter

Silver Supporting Member
Messages
1,910
My preferred solution to the 'V3' issue is a big grid stopper, eg 47k, at the tube socket, or to replace the 1M grid leak with a 470k+470k potential divider.
Another problem that can arise in the reverb channel is that as the cathode bypass cap on V4 ages, a degree of positive feedback around V4 is introduced, which increases with the Reverb control setting.
The bypass cap on V4 is new, but I'll try the grid stopper/grid leak idea next. Thanks!
 

andybaylor

Silver Supporting Member
Messages
3,647
Give this a read. Seriously.

https://www.thegearpage.net/board/index.php?threads/1025072

There's a link to Mr. Phillips original post concerning 16 ohm speakers in a Deluxe as well.

FWIW- To me, the harshness is a quality of a Fender sIlverface guitar amplifier. This is why the Blackface models sell for more money. They sound much better.
Also, I've never heard a "blackface conversion" that sounded as good as the real deal. Waste of time and money, IMO.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

You might be amazed by this, but actually 16 ohms is a better match for a Deluxe Reverb than 8 ohms is. Really! Fender made them like that for some reason... the actual 'correct' match going by the OT turns ratio is somewhere around 13 or 14 ohms if I remember rightly, but 16 is close enough.

No, I didn't believe this at first when I read about it either - but I checked it using different loads and metering the output power at each. Sure enough, more power was produced at 16 ohms than 8, which indicates a better match. In fact, the stock 8-ohm load is a better match if you put 6L6s in the amp...

Assuming the OT
is an exact reproduction of the old spec, what you should get is slightly more power, and a tighter, more controlled and even tone with less flub at the bottom end when it's pushed hard. And definitely no risk whatever.
 

pdf64

Member
Messages
8,056
Whilst there's no reason to disbelieve John Phillips' finding, consider that we only seem to have his conclusion on an investigation on one particular amp, and that for that one amp, the tolerances of its component parts may have lined up to produce an unusual performance characteristic.
We don't know anything about the test conditions, eg test equipment, line voltage, how many sets of power tubes were used etc.
It may be that only one pair of 6V6 were used and that they were somewhat past their best and so better able to drive a less demanding load.
Note only 'slightly more power' is claimed, a more exact figure is not mentioned.
To extrapolate the conclusion of that one report to cover every DR may be overly credulous.
 

twangbanger

Member
Messages
1,492
I used to run a 16ohm tone tubby in my SF deluxe reverb for a few yrs w/ no problems. I could then run a 2x12 16ohm cab w/ it on some gigs.
 






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