Deluxe Reverb servicing, I need some help.

tubedude

Tele-Afflicted
Joined
Jul 26, 2013
Posts
1,358
Location
east georgia
Wow, I found imobile.com on a search and they told me which secret key sequence will fix my computer, and it worked!



Tube Dude, thanks. I don't think this cap is even in the audio chain..when you say these caps will out-perform electrolyte caps, in what way do you mean out-perform?
In every possible way. They have lower ESR, their faster, they have no paste electrolyte to dry out so last forever, they are tighter tolerance, they don't drift as they age, if subjected to high voltage spikes they self heal instead of shorting out. Look at a spec sheet for the specifics.
 

Lowerleftcoast

Poster Extraordinaire
Joined
Dec 30, 2019
Posts
6,239
Location
california
I just checked the 100 kOhm half-watters, in circuit, they all read the same: 107-108 KOhms. Would they all go out of spec in the exact same fashion?
Most of the plate resistors get hot so they get a workout. They typically drift up to ~110k, which is OK. Indication to replace them is a hiss or frying bacon type sounds. If they get a hairline crack, they will make a *pop* type sound. Chopsticking will usually reveal a cracked CC.
 

WalATX

TDPRI Member
Joined
Nov 10, 2013
Posts
96
Location
Illinois
In every possible way. They have lower ESR, their faster, they have no paste electrolyte to dry out so last forever, they are tighter tolerance, they don't drift as they age, if subjected to high voltage spikes they self heal instead of shorting out. Look at a spec sheet for the specifics.
Agreed ^

Checked back in, lots of good info in this thread. Reminds me of the maxim, “no two of a trade agree.”

Film, mica & tantalum > electrolytic, typically. Small caps are usually not electrolytics because the cost is low enough to justify. Electrolytics are cost effective for larger capacitances (like 25uF for example), and good electrolytics should last over a decade if not longer. The main question is, if you want to do this recap/repair just once, is it worth spending the extra $ to upgrade? For many it is.

I wouldn’t use no-name electrolytics, or any no-name parts, personally. You might save $10 once a decade? Not worth it imho.

Wima, Kemet, Panasonic, Nichicon, Elna Silmic, Sprague, Mallory, SoZo, F&T, etc. All quality brands.
 

Blue Bill

Doctor of Teleocity
Ad Free Member
Joined
Feb 15, 2014
Posts
10,269
Location
Maine
Thanks guys. I just ordered some parts from surplussales.com. Wow, they have everything. Worth a look.

On allelectronics.com, I found a chassis-mount dual fuse block for AG fuses, but can't seem to be able to find the info on which fuses to put on the PT leads, oy. Was it 2 amp slo-blow? They have a 6uF metal-film cap, I'll give that a try in the reverb circuit.

Also, it turns out there are zero mounting bolts on the grommet board, it's just been flopping around. Does anyone know where to get half-inch 6-32 nut and bolts with the attached star washer? I haven't been able to locate any. I've spent hours researching and not much time actually fixing up the amp, Im itching to fire up the soldering gun and make some progress. 6uf.cap.jpeg fuse.block.jpeg
 
Last edited:

WalATX

TDPRI Member
Joined
Nov 10, 2013
Posts
96
Location
Illinois
…but can't seem to be able to find the info on which fuses to put on the PT leads, oy. Was it 2 amp slo-blow?
I have used 1A slow fuses in my AB763 (similar power usage). Maybe get a 1A and a 2A, and if the 1A blows swap to the 2A.
Does anyone know where to get half-inch 6-32 nut and bolts with the attached star washer?
I go to my local Ace hardware or other small parts store. Usually they’ll have enough selection to find something that works.
 

Blue Bill

Doctor of Teleocity
Ad Free Member
Joined
Feb 15, 2014
Posts
10,269
Location
Maine
Thanks, WalATX. I just ordered a 5-pack each of 1A, 1.5A, and 2A fuses, with the fuse block and 6uF cap.
 
Last edited:

Blue Bill

Doctor of Teleocity
Ad Free Member
Joined
Feb 15, 2014
Posts
10,269
Location
Maine
Try Rob's site. Look under *Amp Protection Mods*.

There are fuses for the heaters and for the PT. Both are shown on the site.
Thanks LLC. Maybe it's me...I tried for 30 minutes to dig out any info on fusing the high voltage secondary leads on the PT, I think it's just not there. https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Protection_Mods

There's a photo of an impressive amp layout, copied below, built by Marcus Albrecht, which shows the pair of fuses between the transformer and the rectifier tube, which makes sense to me, but I can not find any indication of the amperage rating for the fuses. There must be 500 mods listed, I scrolled through them all at least twice, till my eyes crossed. I'll follow WalATX's suggestion and try 1A, and go up to 1.5 then 2 if they blow.

Deluxe_Reverb_Chassis_by_Marcus_Albrecht_small.jpeg
 

WalATX

TDPRI Member
Joined
Nov 10, 2013
Posts
96
Location
Illinois
I'll follow WalATX's suggestion and try 1A, and go up to 1.5 then 2 if they blow.
Blue Bill, I remember having the same problem finding info on the fuse ratings when I built my AB763 kit.

Nevertheless, I’m almost certain I found that “1A” fuse rating on the Valve Wizard site, which gave me some confidence. I believe he wrote that amps less than 60 watts rarely need more than 1A between the mains and PT. Better to err too small and work your way up, than to have a fuse so large it doesn’t shut things down during a fault.

In any case, I have run that kit for months on 1A so it is working for me. Good luck!
 

Lowerleftcoast

Poster Extraordinaire
Joined
Dec 30, 2019
Posts
6,239
Location
california
Maybe it's me...I tried for 30 minutes to dig out any info on fusing the high voltage secondary leads on the PT, I think it's just not there.
It's there... this from Rob's 5F6A mods site:
"Amp fuses suggested by R.G. Keen: 300 to 500 milliamp slow blow fuse for the 5F6A to the power transformer high voltage center tap (B+ Fuse). 200 to 300 milliamp for a 5E3. 4 amp slow blow fuses added to each 6.3v heater line (2 parallel fuses = 8 amp limit). 4 amp slow blow fuses added to the rectifier's 5v heater lines. I don't recommend a fuse on the power transformer's bias tap because if it blows the power tubes will run away with max current and burn up. I highly recommend you at least install the B+ fuse to protect the power transformer."

And... this is added to the above from Rob's Generic tube amp site:
"Marshall likes to use a 500ma fast blow fuse in each of the high voltage secondary wires (not shown above) in their 50 watt amps, and 1 amp fuses in their 100 watt models. Just insert them between the power transformer and rectifier tube. An amp with a pair of 6V6 power tubes would use a 300ma fast blow fuse."

So... fusing the heater lines... R. G. Keen suggests 4 Amp slow blow in one or both *sides* of the heater line depending on if the heater has an artificial CT. Fender "57 Deluxe" schematic/layout shows this arrangement when using an artificial CT.

There are two methods discussed for protecting the HT secondary. The first method adds a slow blow fuse to the HT center tap. For a 6V6 style amp 200mA to 300mA is discussed.
The second method adds fast blow fuses to each HT secondary. The suggestion is for 500mA fast blow fuses for a 50W Marshall. Since the Deluxe Reverb draws less current smaller fuses could be considered.

The Valve Wizard has some different views. This from his *Fuses* article...
"When a fuse melts, an arc will be sustained until the gap widens enough to quench it, or until the voltage drops to the point where the arc cannot be sustained. With AC this happens very quickly since the voltage is continually passing through zero, but with DC the arc will be sustained for much longer. In other words, it is easier and safer to interrupt AC than DC. Therefore, the fuse should always be placed in the AC part of the circuit, before the rectifier, where possible."
"An argument can be made for not fusing the heater winding, provided it supplies nothing but AC heaters and lamps. You know, simple stuff. There is very little to go wrong with a simple AC heater supply, and the likelihood of a fault creating a permanent short is slim. Also, the inrush to heaters at switch-on is so heavy that it may be difficult to find a fuse that will withstand it. I've never seen a 20mm fuse rated at more than 10A. Beyond this you might consider automotive fuses. Traditional amp designs don't use heater fuses, and I have never heard of it being a problem.
However, if the heater supply has a rectifier for DC heaters or ancillary circuits then fusing is suddenly and strongly recommended; rectifier diodes nearly always fail short. If this means adding inrush-limiting to achieve a soft start and stop the fuse from blowing every time you switch on, so be it."

Here is Blencoe's HT fuse suggestions for PTs with and without center taps.

Fuses3.jpg
 

Blue Bill

Doctor of Teleocity
Ad Free Member
Joined
Feb 15, 2014
Posts
10,269
Location
Maine
LLC, you are the man. (Pardon my gender-insensitivity, assuming your pronouns :oops: ) I did see those, but in my overwhelmed state, at midnight last night, I dismissed them as pertaining to different amps than the DR, and therefore, perhaps not correct for it. It looks like the money paragraph is:

" There are two methods discussed for protecting the HT secondary. The first method adds a slow blow fuse to the HT center tap. For a 6V6 style amp 200mA to 300mA is discussed.
The second method adds fast blow fuses to each HT secondary. The suggestion is for 500mA fast blow fuses for a 50W Marshall. Since the Deluxe Reverb draws less current smaller fuses could be considered. "

Now that I ordered 15 slo-blo fuses, at least they don't cost much, I'm on my way to the hardware store for the chassis mounting screws. I'll see if they have 300ma fast blows. I guess I should pick up a pair of 1/2 ampers too, in case the smaller ones pop erroneously.

I agree with the Valve Wizard, that the lower-voltage PT leads have less risk of causing major damage. Thanks again!
 
Last edited:

CoolBlueGlow

Tele-Afflicted
Joined
Nov 20, 2011
Posts
1,599
Location
Arkansas
Beware, you will have increased high voltage if you replace the 5U4 with a 5AR4 or GZ34, requiring a rebias of the output stage.
I'd replace the speaker.


Agree that a rebias will be in order, but is probably in order anyway. The significant advantage of using the GZ34 is that the filament load is 1.1 amp less than a 5U4. That 1.1 amp lower strain on your 50 year old main transformer is a significant lessening of filament winding load. Since the heat between all secondary windings is quickly shared inside the transformer, ANY reduction in any secondary load is good for the lifespan of all secondary windings. Cool transformers live longer.

Keep in mind that the GZ34/5AR4 is an indirectly heated cathode, whereas the 5U4 family is a direclty heated cathode. That's also a good benefit in this case generally beneficial to component logevity, due to the slightly gentler rise to operational B+. Going the other way, (changing from GZ34 to 5U4 and similar) not so much...

In my experience, there are three other mods that are good investments in OEM transformer longevity. In my practice, I always add these three. All are undoable and do not affect the vintage vibe of the amp.

1. A small cooling fan mounted to the primary transformer. It can be powered by a wall wart or even from a small rectified source from the filament circuit itself, if sufficient headroom is present. If you swap to a GZ34, you just gained 1.1 amp headroom. You can invest 100 (or less) of that in powering a quiet 12vDC computer CPU fan. The cooling provided will reap transformer life benefits far in excess of the >100ma load the fan imposes.

2. I add a heat sink - attached directly to the bell of the transformer. Epoxy+ thermal compound is your friend, unless you are an absolute purist and cannot see your way clear to remove the varnish drippings from your transformer bell. :) For those guys, rig a non-destructive bracket to existing screw and just use thermal compound. TIP: Heat sinks can be harvested off old dead computer CPU. They work great. Many have 12vDC fans integrated into them, which is even nicer and which solves the fan-mounting issue in one fell swoop. I always install a bypass switch on the fan, for those times that my amps went to the studio for recording, and where a fan noise is unacceptable.

3. I always include a bucking transformer for amplifiers in this age range or older. This is built into a standard 2 gang box and stuck in the back of the amp. This simple tool reduces primary transformer input voltage to about 115VAC, which helps restore plate voltages to something a little more normal. Primary dropping like this will also bring your tube filament voltage back into reasonable range. This is almost universally ignored by guitar amp guys, but it is an improvement that will gain benefits for tube longevity - if you have an amp that is already pushing the filaments beyond their "best" range.

These are all minor improvements. Some guys overlook or dismiss them. They are not sexy like speaker swaps, tone stack, feedback mods, special PIO caps, grain oriented magic wire, mystery tibetan salt crystals, , and so forth. But they are easy to accomplish and are all good performance and safety measures - ESPECIALLY if you are going to be driving a vintage amp hard for regular shows. (Something I personally did my entire active career as a player. I never blew a vintage amp so modified in 30+ years of gigging them this way)

Finally, speaking of speakers, I FULLY agree with TubeDude - definitely replace that speaker. IME, this is just not a great match for a Deluxe, and EV units are very heavy too. I've been down this road of these large voice coil high performance PA style speakers in small tube amps. Besides the JBL D123, I've had poor results with this particular path, and FWIW I have about fifty or sixty of these types hanging on my speaker wall of fame/shame. The lower power "primative" types just seem to work better in Deluxes.
 

CoolBlueGlow

Tele-Afflicted
Joined
Nov 20, 2011
Posts
1,599
Location
Arkansas
That is an Ashton cap Doug is testing, the straw man is I am talking about blue molded caps…..that’s the topic. Remember?

again show me a blue molded cap that shows leakage, that’s will that will be a first, I have seen plenty of leaking ashtrons, and mustard caps.

I have 50 blue molded caps right now, around 60 years old, none leak, another straw man, never said they never leak, I said show me one, it will be my first, I have tested 100s


nothing but straw man argument from you, while you accuse me of this?…..another added to the ignore list, congrats
offer stands, I will test any blue molded cap for leakage….on a stancore capacitor analyzer. If it’s bad, it will be a first.

bell labs, who designed the blue molded capacitor, back in the day , had the nickname hells bells, it was the birth place of the transistor, the idea of the jfet also started at bell labs, but was perfected elsewhere, like I said, one of the best labs in the world, made a great small signal capacitor. Nothing magic …..
Interesting disagreement over capacitors. Not picking a side, but here's a tiny sliver of data to throw into the discussion...

FWIW, based on your comment that you said you'd never had a bad one, I got to wondering. Gee, had I? I had a sort of feeling by experience that the blue molded caps rarely failed, and rarely seemed really leaky, but was that seat of the pants feeling accurate?

So, to get that answer I just bench tested ~20 Blue molded caps I had lying about. They were removed over the past 30 years from various amps because they were old and suspect, but were ultimately kept in my junk bin because they were not proven defective. Most, if not all, came from Fender amplifiers.

These samples were from Circa 1960-1965 era amplifiers. Test fixture conditions were as followed

TESTER: a well-calibrated Sprague T0-6.
CALIBRATION REFERENCE: The T0-6 was first checked with calibration reference capacitors. They were a set of three General Radio T505 - measured solo and in combinations of 1, 2 and 3 in parallel. I checked the .02-.5 range on the TO-6, which gave exactly .02, .04 .059 and .078. I checked the .1 -.5 range with the stack of three ref caps, which together showed just a breath under .1 (when measured on the .1 scale.) This is well within the advertised accuracy of a Sprague T0-6, which is +3%/-5%. Leakage of all three calibration reference capacitors was then measured. They returned indicated zero uA on the TO-6 leakage meter, when set at .06 mA (max sensitivity), and driving the calibration capacitor at 400VDC. A reading of 1 mark on the meter movement at this setting is equal to one microamperes. That's pretty low.

Finally, I verified that the test system was sensitively detecting real failures by checking one known bad capacitor, which easily showed high leakage, as expected.

Using this measuring system, 375-400VDC was then gradually applied to each blue molded, and that voltage was monitored by a HP 3466A. The capacitors were then discharged and checked for accuracy of value. 400V rated caps were never pushed over 375. 600V rated caps got the full 400VDC.

RESULTS:

Using this fixture, the ~20 blue molded caps I tested were remarkably consistent in leakage. Each one showed between ~30 and 50 uA of leakage. The blue molded capacitors were generally close to spec, but with many of them testing a bit under marked value (with the reference being a set of three General Radio laboratory calibration capacitors) but a few testing above marked value. This is normal and expected behavior, IME.

For grins I then compared about ten Astron (yellows) from the same era, as well as some of those teal blue jobs commonly used in Silvertone amps. (all amp techs let out collective groan) The Astrons were measurably worse, averaging between 70-120uA, and the teal blue jobs were all over the place, always worse than the blue molded versions, occasionally better than Astrons but often worse. I only had six of these, though...but that's because I threw away dozens over the years because they were so prone to failure (in my experience). So, not a significant sample size.

So, from my measurements, my small sample of twenty-ish sixty year old blue molded capacitors uniformly leaked a very small amount of current, and were mostly close on value as marked.

To be fair, 30-50 uA is not much leakage, but it is not zero, either.

Just my results - conducted just now 11/18/22
 

Blue Bill

Doctor of Teleocity
Ad Free Member
Joined
Feb 15, 2014
Posts
10,269
Location
Maine
Agree that a rebias will be in order, but is probably in order anyway. The significant advantage of using the GZ34 is that the filament load is 1.1 amp less than a 5U4. That 1.1 amp lower strain on your 50 year old main transformer is a significant lessening of filament winding load. Since the heat between all secondary windings is quickly shared inside the transformer, ANY reduction in any secondary load is good for the lifespan of all secondary windings. Cool transformers live longer.

Keep in mind that the GZ34/5AR4 is an indirectly heated cathode, whereas the 5U4 family is a direclty heated cathode. That's also a good benefit in this case generally beneficial to component logevity, due to the slightly gentler rise to operational B+. Going the other way, (changing from GZ34 to 5U4 and similar) not so much...

In my experience, there are three other mods that are good investments in OEM transformer longevity. In my practice, I always add these three. All are undoable and do not affect the vintage vibe of the amp.

1. A small cooling fan mounted to the primary transformer. It can be powered by a wall wart or even from a small rectified source from the filament circuit itself, if sufficient headroom is present. If you swap to a GZ34, you just gained 1.1 amp headroom. You can invest 100 (or less) of that in powering a quiet 12vDC computer CPU fan. The cooling provided will reap transformer life benefits far in excess of the >100ma load the fan imposes.

2. I add a heat sink - attached directly to the bell of the transformer. Epoxy+ thermal compound is your friend, unless you are an absolute purist and cannot see your way clear to remove the varnish drippings from your transformer bell. :) For those guys, rig a non-destructive bracket to existing screw and just use thermal compound. TIP: Heat sinks can be harvested off old dead computer CPU. They work great. Many have 12vDC fans integrated into them, which is even nicer and which solves the fan-mounting issue in one fell swoop. I always install a bypass switch on the fan, for those times that my amps went to the studio for recording, and where a fan noise is unacceptable.

3. I always include a bucking transformer for amplifiers in this age range or older. This is built into a standard 2 gang box and stuck in the back of the amp. This simple tool reduces primary transformer input voltage to about 115VAC, which helps restore plate voltages to something a little more normal. Primary dropping like this will also bring your tube filament voltage back into reasonable range. This is almost universally ignored by guitar amp guys, but it is an improvement that will gain benefits for tube longevity - if you have an amp that is already pushing the filaments beyond their "best" range.

These are all minor improvements. Some guys overlook or dismiss them. They are not sexy like speaker swaps, tone stack, feedback mods, special PIO caps, grain oriented magic wire, mystery tibetan salt crystals, , and so forth. But they are easy to accomplish and are all good performance and safety measures - ESPECIALLY if you are going to be driving a vintage amp hard for regular shows. (Something I personally did my entire active career as a player. I never blew a vintage amp so modified in 30+ years of gigging them this way)

Finally, speaking of speakers, I FULLY agree with TubeDude - definitely replace that speaker. IME, this is just not a great match for a Deluxe, and EV units are very heavy too. I've been down this road of these large voice coil high performance PA style speakers in small tube amps. Besides the JBL D123, I've had poor results with this particular path, and FWIW I have about fifty or sixty of these types hanging on my speaker wall of fame/shame. The lower power "primative" types just seem to work better in Deluxes.

Hi CBG, thanks for checking in. You have some good ideas. I'll be re-setting the bias anyway, I want to clean out the bias pot. Plus, a few months ago, I picked up a matched pair of Telefunken 6V6s, on sale, which I'll give a try. I like the idea of a bucking transformer; there was a recent thread here about that. Also, thanks for sharing the results of your capacitor testing project.

We may need to agree to disagree on the speaker. I just love the sound of the old EVs. The extra punch and growl suits me to a T. I would consider a JBL, but I already have the EVM.
 
Last edited:

Lowerleftcoast

Poster Extraordinaire
Joined
Dec 30, 2019
Posts
6,239
Location
california
assuming your pronouns
You got the proper pronoun. lol.
I guess I should pick up a pair of 1/2 ampers too, in case the smaller ones pop erroneously.
Chances are your PT is rated for less than 150mA and the amp will use less than that. The main point is to protect the PT wire from heating to the point of failure or melting the enamel insulation. You don't want nuisance tripping so you want a value large enough to avoid metal fatigue of the fuse yet small enough to trip when needed. I assume most of the time the circuit will have a catastrophic failure. It won't just slowly heat up. The diode will fail short or the tube will fail short to the heater. Maybe others will opine differently but I would think 500mA of fast or slow blow fusing would suffice. Either will trip with the *event*.
 
Last edited:

Blue Bill

Doctor of Teleocity
Ad Free Member
Joined
Feb 15, 2014
Posts
10,269
Location
Maine
Well, I finally got sone actual work done this weekend. Installed the new 6uF cap, which is huge and really bright yellow. I switched out the 6 100K resistors in the preamp front end. Replaced that big red mica .001 cap with a smaller .001 disc cap. While I was at it, I replaced the 2 10K 3W resistors in the doghouse with some modern 5%ers. I removed the old power cord and death cap, and replaced them with a nice bright red 14-3 cord from Mercury Magnetics. I completely bypassed the ground switch, instead, I used the lugs on the convenience outlet as a connection point.

The fuse that has been in the fuse holder for a couple decades is a 2A SB; I replaced that with the recommended 1.5A SB. I installed the dual fuse holder and wired the fuses between the secondary windings and the rectifier tube. Plus, I investigated the eyelet boards for conductance; I couldn't detect anything that looked problematic.

I'll fire it up through the light bulb limiter and look for smoke, maybe later tonight or tomorrow. I watched some Psionic Audio videos, recommended by @TeleRooo, wow they're packed with good info. Now, I'm itching to crack open my 68CDR and fix all the weaknesses he pointed out in these PCB DRs. I'm having a blast learning more about amps and getting things fixed up. Thanks again you guys for your input and helpful support.

Does anyone have a source for guidelines on lead dressing? I'll try looking it up. It seems like a lot of the wires in this one are kinda too long. Thanks.

IMG_1952.jpg
IMG_1954.jpg
IMG_1953.jpg
IMG_1950.jpg
 
Last edited:

Blue Bill

Doctor of Teleocity
Ad Free Member
Joined
Feb 15, 2014
Posts
10,269
Location
Maine
So far, everything is working fine. It's nice and quiet, no sizzles or pops, I gently thrashed around with a chopstick, no signs of trouble.

Now, the real question: How important is it to go through all the rigamarole necessary to calculate the bias current? Is it nuts to just set the bias pot middle lug to -35 vdc, then stare at the tubes and look for redplating? I wonder how critical it is, when most discussions include the option of running the bias voltage up or down some unspecified amount, if you want it "hotter" or "cooler".

People talk about protecting tubes from stress to maximize tube life, I get it. I've had this amp for decades, and I've tried dozens of 6V6s to see which sound better, but I can't remember ever having one fail. The old G-Es that are in it now have been there since last century and they seem fine. I've switched tubes without checking the bias many times, and it's never eaten a tube. Please let me know if I'm a big ignoramus.
 

Blue Bill

Doctor of Teleocity
Ad Free Member
Joined
Feb 15, 2014
Posts
10,269
Location
Maine
I hooked up the cabinte with the EVM and plugged in a Strat. It sounds really good, nice and loud. The only issue: the low E string, played open, is a little farty, not horrible, but saggy and flabby. It is fine on volume knob setting from 1 to 6, flabs out from 6 to 8, then tightens back up at 8-10. I almost never play past 7, even outdoors, so cranking it to 9 or 10 is not a good fix.

I tried the new fancy Redbase 6V6GT-STR tubes, not a dramatic change, maybe a little more gain. The G-Es are a nice pair, so I may never find better ones. The STRs had the same saggy issues on volume setting 6 to 8. I may try switching out the first 16uF filter cap in the doghouse with a bigger one, JJ makes a 30uF-500V one that will fit under the hood. Suggestions welcome.
 

Lowerleftcoast

Poster Extraordinaire
Joined
Dec 30, 2019
Posts
6,239
Location
california
It is easy to test more capacitance, just alligator clip in another cap in parallel with the cap. Two 16uF = 32uF...
 




Top