Silverface Deluxe Reverb Cap evaluation

[ndross475]

I am starting a new project.  The PR is performing nicely, thanks to alot of input from members on this board.  Thank you.

I have a 77 Deluxe Reverb no-boost. Looks to be the AB1172 circuit.  When I got it it was as you see it. Filter Caps and bias caps had been changed and that's it. Original speaker was there but torn and rattling so I put in an Eminence Alesandro. Plays nicely but not remarkable.

I am fairly certain I am going to take it back to AB763 specs. I have spent most of this hot day sitting at the computer reading on the process and the many schools of thought. A lot of good stuff here.

I am of the mindset that I don't want to pull anything that I don't have to, or isn't a wise precaution to catastrophic failure so I am looking at replacing the electrolytics and don't want to change the blue caps unless this looks threatening. My understanding is if they fail it isn't catastrophic like some of the elec. I am not worried about them ruining my gig a Royal Albert Hall;-) But those bubbles have me concerned.

So keep em or ditch em...??

I'll post a detailed to-do list and any questions later but this is the one that I am curious about as I prepare my parts order.

This conversion has been detailed a couple of times here so a lot of my questions have been answered. Thanks to all those who worked with those guys.

Thanks,
Nick

[Tony Bones]

The risk with old coupling caps is that they'll leak (electrically.) i.e. not block DC like they're suppose to. But, you can check for that with a DMM. Power the amp up with all tubes removed and start looking for positive voltage where there should be zero. Or, in the case of the output tubes, probe pin 5 (grid) and verify that the voltage there is whatever the bias supply is putting out, and isn't being pulled up by a leaky coupling cap.

There must be instructions for this somewhere on the web...

[ndross475]

Thanks Tony... any experience with bubbles like this? I understand when I see this on the filter caps its past time to swap but what about these?

I kinda was planning to do what you suggested. Test it running and if it isn't leaking don't replace until they do,, unless someone says thats a bad plan...

[sluckey]

That just looks like wax to me. Can you scrape it off with a fingernail?

[ndross475]

@sluckey you are good... That solves that question. Thank you.

Now all I need to do is finalize the list for the elec caps and the 763 conversion....

ill post some pics tomorrow of the before... its pretty clean and all original as far as I have been able to tell.

[Toxophilite]

Out of curiosity why do you want change it to AB763 specs?


I know its prevailing opinion on the internet that all fenders must be blackface, but silver face fenders are fine sounding amps.
Also the deluxe is one of the ones with the least changes


I guess it's relatively easy to change it back if you don't like it

[mresistor]

I think I like where the standby switch is located on the AB763 better than that AB1172  especially if using a 5U4GB. Am I wrong in that thinking?

[jim]

Do you play out with this amp?  If anything, just try replacing the 5U4G with  a GZ34 or 5AR4. The HV will increase by about 20V and will necessitate rebias.  You should also have modern e-caps in place with ratings of 500V.  You will have more brightness, headroom and dynamics.  That Alsesandro speaker is going to sound a lot better pushed a bit more.  If you dont like it its easy to go back. You will get more bang than from any other blackface mods.  Jim

[ndross475]

Out of curiosity why do you want change it to AB763 specs?


I know its prevailing opinion on the internet that all fenders must be blackface, but silver face fenders are fine sounding amps.
Also the deluxe is one of the ones with the least changes


I guess it's relatively easy to change it back if you don't like it.---Mainly this. 

I like the tone of the amp but don't find it remarkable.  Someone else's opinion I trust agreed with the assessment.  As this is a 77, I don't see the harm in changing a few components (if done correctly), not the sacrilege of hacking up a 65 per say. And as you said if I don't like it I can always change it back. I bought this one with the express intent of learning how the parts work and interact... A pricey cadaver. There is so much on this forum and others on that layout that its easy to follow along, see what others have done and why.  I also am interested in learning how the various components "color" the tone. Its pretty easy to read about it, but I learn better by doing.

[ndross475]

I think I like where the standby switch is located on the AB763 better than that AB1172  especially if using a 5U4GB. Am I wrong in that thinking?

As far as I can tell they are in the same place...

[ndross475]

Do you play out with this amp?  If anything, just try replacing the 5U4G with  a GZ34 or 5AR4. The HV will increase by about 20V and will necessitate rebias.  You should also have modern e-caps in place with ratings of 500V.  You will have more brightness, headroom and dynamics.  That Alsesandro speaker is going to sound a lot better pushed a bit more.  If you dont like it its easy to go back. You will get more bang than from any other blackface mods.  Jim

No I don't play out. So absolute reliability isn't as important to me as to some. I am mainly concerned with the health of the amp. And coloring tone to my taste.

I intend on trying the GZ34, and I understand I will have to re-bias.

I agree that modern e-caps is wise and upping voltage to match current amp voltage is the right course. The bias and filter caps have been changed and are upgraded. I have been reading different opinions on what if any affect the f&t 70uf/100v bias installed may have on tone / feel vs the 25/50v called for. Also the filters were changed to f&t 16uf/475 (1&2) and 22uf/500v (3,4,5) Not sure if that was intentional or just what they had. 
I have read the uf change will affect tone / feel and some say it won't be noticeable.  I don't have the experience to know.... yet ;-)

What I am studying now is all the other threads where people discuss where to "upgrade" resistors to film and or / to higher wattage and where to keep original carbons or replace with new higher wattage carbons. Also there is the cap brand A vs cap brand B and their affect on tone discussion.

Studying the voodoo of resistors and caps and various schools of thought has been an interesting way of avoiding the heat.

Since most of the parts I am considering are inexpensive I am considering an exercise where I mic the amp and make changes and then re-mic it just to see if I can really hear it...

a friend asked me why I am doing this and I said I don't fly fish or build model airplanes... gotta pass the time some how and this is interesting... and my toys get loud!!!

[mresistor]

I think I like where the standby switch is located on the AB763 better than that AB1172  especially if using a 5U4GB. Am I wrong in that thinking?

As far as I can tell they are in the same place...

No  look at the two schematics  The ab763 has the standby switch after the first hv filter node thus at turn on the first filter caps are allowed to charge up and yours has it before any of the hv filter caps, when you take yours off standby it results in a very large inrush current and more stress on the rectifier. I like the AB868 too..  If using a 5AR4 which has a considerable delay when ramping up the HV then you can just turn the on switch on and also the standby switch at the same time, in your later sf amp. I have a Hoffman AB763 amp and I do not have a standby switch and it has a 5AR4 recto. I think standby switches are for perfomers that want to cut HV during breaks in performing..   but  why not just turn the volume down.. ?  The amp isn't going to do much with no signal applied. sure it will have hv applied  so... 
You have a standby switch...that's ok  and guitarists have been using them for a long time..   but  do take a look at the differences as to where the first filter cap node is.. and consider what rectifier you are using.. I'm not so sure that a 5U4GB drops only 20v less than a 5AR4 ..  also I'm not really sure why CBS Fender made those changes..
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxereverb_a1172.pdf
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_aa763_schematic.pdf
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_ab868_schematic.pdf

[ndross475]

That was a good observation.. I have read a lot of threads on converting this amp and haven't seen that mentioned. I will do some digging and look into that.  Doesn't appear to be that difficult a change.. I just don't have the experience to know the pro/con and why of the change... But I will def be looking into it... Thanks..

[vampwizzard]

ndross475: I think a common practice in restorations and modifications is to replace only the parts that need replacing. Typically that means capacitors but not always if youve got an ESR meter and are willing to measure everything and trust your results.

That being said, if its a conversion and not a full strip down build up id leave the dang resistors as they are and replace with those of a similar type. I've preferred metal vs carbon in my new builds but if it worked for Leo and thousands of musicians for 30-40 years who am I to argue?

Keep us posted on the results. Looks like an interesting project.