Modifying 1979 Silveface Deluxe reverb to Blackface vintage.

[LoveChet]

According to literacture I am told that if I have a Deluxe Reverb made after 1976, a blackface mod will not give you the benefits unless the transformers are changed, and that the cost isn't worth it. Mine is a 1979 Silverface with some mods already.

So, what would I be up against if I decided to change transformers and do a blackface mod. I assume power transformer as a minimum. Can you get them? Possibly output transformewr as well ?

I am sort of committed to this amp as its a grudge thing at this point. I've got it sounding fairy good by changing the 6V6 output tubes (tungsol) and setting bias to 21ma to start with. I also have changed all other small tubes plus 5U4G power tube. Ive just rekindled my electronics background and starting opening it up and making measurements. Also I have other modes already in place. I have an effects loop, master volume, and a 6 position fat switch all installed by Paul Revera. Recently I traced out the effects loop mod and made a schematic of it and then debugged it since it wasnt working. It has an extra 12AX7. There was a short between two added components and also the pull switch in the pull switch/return pot was dirty and open. Right now I am running a BigSky reverb in the loop as a Plate Reverb. I don't like the effect of the onboard spring reverb. I am assuming I should be able to get a good sound out of this amp since Paul Yandell and Chet Atkins recommended it to me. They didn't however specify a pre 1979 silverface or a blackface.

Thanks

[Justin Thomas]

Given all that other stuff that's been done I hesitate to call itva Deluxe Reverb anymore...

Given that the AB763 & 1977 Deluxe Reverb schematics both list an AC output of 330V & a B+ of 420, I don't see why a new PT should be necessary... In the smaller amps the bigger changes were in the cabinets.

I'd say blackface away... Not sure whether you want to keep all the extra stuff. You could just make it a "regular" Deluxe & not have to worry about the extra tube if you don't like onboard reverb anyway. Just repurpose the reverb tubes already in the amp.

Justin

[LoveChet]

I agreee its no longer a deluxe. I do want to keep the mods since in the long run I think it will help the tone based on who recommended the mod.

But like you said maybe I should do the mod anyway and not worry about the transformers.

You meantioned AB763 & 1977. The link below for one silverface to blackface mod says that 1976 was the cutoff date of manufacture after which you wont see benefits from the mod, due to transformer changes made by CBS after 1976. Mine was built in 1979.

https://schematicheaven.net/mods/silver2blackmod.html

Thanks for feedback

[Justin Thomas]

That link is a blanket statement that covers "most" amps. Comparing actual schematics is the way to go. The two I referenced are specific to the Deluxe Reverb. And the 1977 refetenceis the year that schematic was issued. AB763 was 1963. And the tranny specs didn't seem to change.

Justin

[LoveChet]

What are the two circuit diagrams I need to know what Im dealing with. Is one for the blackface that I want and the other the silverface that I have. In snooping around in my amp I found that I have .001 K caps from both 6V6 control grds to ground. I found a diagram with those shown. From what I have read those are for suppressing oscilations due to some of the changes made when they went to silverface. That makes me think Im dealing with higher voltages and therefore bigger transformers. However there are zillions of diagrams out there and I dont know which apply to me. Like I said, near as I can figure my silverface was made in 1979.

Gary

[eschertron]

In snooping around in my amp I found that I have .001 K caps from both 6V6 control grds to ground. I found a diagram with those shown. From what I have read those are for suppressing oscilations due to some of the changes made when they went to silverface.

Gary,
I looked over the list you linked to. As Justin says, it is a generalized list of possible fixes for possible problems. Do not take it as a magic formula for mojo. Each mod can address a specific issue. Nothing more.

I have SF amp from 1976, and yes, CBS added a small-value cap to ground (actually to cathode on this cathode-bias amp) to suppress oscillations. Well, the internet lore that I ascribe to as truth says CBS added these caps to ALL amps because sometimes, some of them could get HF oscillations due to lead dress or other conditions. Often enough that CBS wanted to NEVER have a warrantee service on an amp for this dead-simple cause. So there's a slight chance that taking these caps out will cause a harsh, gritty response due to parasitic oscillation, but you can only find out one way. If you think the amps needs more 'sparkle' then clip them out. And if you don't like the way the amp sounds with the extended HF response, put similar caps back in. As I said, dead-simple.

Making coupling caps smaller is a time-tested and designer-approved way of 'sculpting' out some LF response. Again, no reason not to make them smaller if there's too much flabby bass. For your ear, for your amp, you may need to try an assortment of values before finding the right one. It's a matter of taste more than anything else. This assumes that flabby/farty bass is a problem that your amp actually has (audible especially at higher gain levels).

Each of these mods can be researched independently. I suggest deciding what your amp lacks, then seek a specific fix. Holy Grail tone questing will always lead in ever-widening circles. Never to your destination. And I don't mean that to sound depressing. Just work towards well-defined deliverables

[g1]

I agree with Eschertron. Try to fix whatever you find lacking in the amp. Maybe there is something wrong with it.
A silverface may not sound 100% as good as a blackface, but it should get you pretty close. To me it sounds like it is nowhere near close.
It would be terrible to go through all that blackfacing and transformer swaps and find out there is still some problem.

[Justin Thomas]

Though I say we stop all this crazy-talk about tranny swapping... Anybody wanna check the schematics after me?

Justin

[Tone Meister]

Though I say we stop all this crazy-talk about tranny swapping... Anybody wanna check the schematics after me?

Justin

I'm not looking at the schematic, but from memory, the dropping resistors in the doghouse are different values making the silverface preamp voltages higher. Restoring ALL voltages to AB763 are the first place to start when "blackfacing" any silverface.

The PT voltages, B+, rectifier choice, and those dropping resistors should be reconciled first to get all voltages consistent with the AB763 schematic, then you can go on to the phase inverter circuit. After that, there aren't too many significant changes with the Deluxe Reverb.

[Justin Thomas]

I didn't check the preamp but the raw B+ feeding the OT was listed as 420 in both. From there it should be pretty easy, and certainly not require a PT change...

Justin

Edit: 1 resistor feeding PI different, though the voltage difference is still well within the 20% tolerance. SF is 10-20V higher.

[pdf64]

I agreee its no longer a deluxe. I do want to keep the mods since in the long run I think it will help the tone based on who recommended the mod.

But like you said maybe I should do the mod anyway and not worry about the transformers.

You meantioned AB763 & 1977. The link below for one silverface to blackface mod says that 1976 was the cutoff date of manufacture after which you wont see benefits from the mod, due to transformer changes made by CBS after 1976. Mine was built in 1979.

https://schematicheaven.net/mods/silver2blackmod.html

Thanks for feedback

From the link

The bad news is that, (generally speaking), if your amp was made after 76, the blackface conversion will do little to help your amp

I think you aren't putting sufficient weight to the 'generally speaking' bit
This is probably the original schematic for your amp https://el34world.com/charts/Schemat...oost_schem.pdf which is the 'pull boost' 1977 version mentioned earlier.
The PT's Fender code is noted as the same 025130 / 125P23B as previous DR versions, eg https://el34world.com/charts/Schemat..._schematic.pdf
I'm sceptical about the nominal HT voltages either side of the rectifier being the same in both versions, as on the face of it, the same Vac input can't result in the same Vdc output for both a GZ34 and a 5U4. The 20% tolerance on the nominal voltages makes them kinda pointless if it's taken at face value.
We can't assume that the Fender part code doesn't mean that the spec is the same from one batch to the next.
But in this case, as long as the PT is used with its intended rectifier type, and the intended Vac mains is supplied, then the HT (and so the amp's power output etc) probably should be reasonably similar year on year, from one version to another. So no reason to consider changing transformers.
How about reporting on the codes of the transformers in your amp?

Regarding the on board reverb, be aware that its characteristics / quality is dependant on the particular reverb tank in there. Diffeent spec tanks have different delay times and degree of reverb effect 'density'; and there's a lot of variance between tanks of the same spec. A more plate like reverb may be obtained with a 6 spring medium delay tank, compared to the 4 spring long delay stock type.

...this cathode-bias amp...

Great post, but just to note that DRs are, as designed, a fixed bias amp.

[Helmholtz]

This list: https://schematicheaven.net/mods/silver2blackmod.html contains errors/ wrong explanations of consequences.

[Chuck H]

Just a couple of things.

If the on board reverb wasn't to your liking and you wanted an effects loop, why didn't you just ditch the on board reverb circuit and build the effects loop with the existing tubes in the amp? It sounds like there are some superfluous circuits in there at this point. Just more to go wrong IMO and it certainly complicates black facing the amp because...

Following a black face LAYOUT is going to be an important part of the effort. Some of the difference between the BF and SF amps seems attributable to lead dress.

+1 on what pdf64 said about the on board reverb. There's no reason it can't sound good. Most do, right? Unless you're committed to the effects loop for other effects and just don't like reverb in general I might suggest rebuilding the amp entirely to stock BF format with the existing transformers. Then fine tune it if the tone isn't suitable.

Speakers are super important. Fender used Jensens and Oxfords. A couple of different models too throughout the life of that amps production I think. Getting the speaker right for the particular Deluxe Reverb tone your after would be more critical than the power transformer in my opinion.

And lastly, you could do as has already been suggested and simply address the amp as it is. What is it not doing for you? Why do you think that black facing the amp will give you what's missing? If you can hear, for example, that the amp has too much LF through the preamp, black facing the amp will not solve for that. Of if the amp is too "harsh". That could be a matter of changing a single capacitor or the speaker rather than a full rewire. So, what is the amp NOT doing for you now and what is the easiest way to get that?

Just a quick nod to the fact that Fender actually reissued the silver face Deluxe Reverb. The '65 is said to be a good sounding amp as is their custom shop 68 version. And the DR is one model where even Fender BF lore and mojo lunatics agree never really changed much compared to other models. So...

Your post runs a little long on the history of the amp, how it has been changed and how you would like to continue changing it. But what is wrong with it?

[eschertron]

just to note that DRs are, as designed, a fixed bias amp.

Right. Sorry if I caused confusion with the pronoun 'this'. I was referring to my amp, where the cap goes from grid to cathode, instead of grid to ground.

[Justin Thomas]

Hey Chuck,

FYI, those 68 Customs are neither Custom Shop nor Reissues. They incorporated some very popular & time-tested mods (tone stack caps, neg feedback, reverb on both channels, etc.) and then dressed them up in 68 SF clothes. But I very much doubt Fender would reissue the amps that likely are what ruined the reputation of the original SF line, wht with that wonky mixed-bias system & themcathode resistors & junk...

That saud, they're pretty nice for a new-production amp, construction being identical to the 65 reissues.

Jusrin