Rescue project: 1972 Twin Reverb silverface

[jeff_free69]

Greetings,

A few months ago I came across a 1972 Twin Reverb, kicked to the curb along with some old furniture.  Skeptical me says it must be completely shot, but how could I leave it there to get tossed into a garbage truck? If nothing else, its a cool speaker cabinet. FYI  I'm familiar with the basic safety considerations when working inside hi-voltage tube amps.  Just haven't done any real repairs here...

After a bit of research (checking the SN# on the chassis and transformer) I'm fairly certain it was built in early 1972.  Its a Silver Face with a Master volume (no push /pull), Utah speakers and casters.  I found several schematics online, the closest being one labeled "CBS... 100 WATTS RMS AMP W/REVERB AND VIBRATO" . drawing 010182 RevC  (shows Master Volume / NO pushpull)


You can find the schematic  here:
https://el34world.com/charts/Schematics/files/Fender/Fender_twinreverb_sf_100_mv_noboost.pdf

The overall condition is ok, just VERY dirty and dusty.  I'm guessing its been sitting buried in the basement for a decade or two.   I've done  some cleanup and exploratory surgery.

After a couple months of video watching and forum researching I am encouraged  to see the rich abundance of information and, more importantly, availabilty of parts.  I've become fascinated by the point to point wiring and could definitely see myself doing new tweed style build later.  For this puppy I originally  thought I'd just plug it in and see what came out  - music or smoke.   But now I realize there are some basic things that could make a big difference. 

Tubes:
The preamp tubes are a mishmash of rca, and (mostly) unbranded. All (4) 6L6 power tubes are Ruby "matched" (interesting that 2 are slightly larger !), so obviously also replaced.

Pulled the chassis, also looking mostly OK

Doghouse' Electrolytic filter caps:
The (3) big blue Sprague Atoms 20uF have dates that I think indicate '96. 
The (2) 70uF/350V have already been replaced, also Ruby parts.  So I assume we're looking at components already 20+ years old and the rule of thumb is to replace them , correct?

Heres where I found a problem:  one of the original big blue Sprague Atom 20uF caps had a broken connection  - the leg pulled right out of the solder joint.  Note that when I pulled off the lid, there was some unexpectedly sticky foam between the lid and the caps.  I was gentle, but I had to pry it off, so its not impossible that this pulled the cap up.

Being that I know just enough to be dangerous, for this first phase I'm leaning towards sticking to the original design, and consider Blackfacing mods at a later date (unless there are some no-brainer best practices you can recommend here)



part I
a. Rewire the power cord / remove death cap and ground switch etc

b. Doghouse electrolytic filter caps
    20uF 500V F&T's (The Atoms are too hard to track down and expensive)
    70uF 350V Ruby's

Bias / recitfier section :  since this is a critical section it seems prudent to replace :
c. (2) 50uF 70V electrolytics in rectifier / bias section : Ruby 50uF 100V
d.   1k 1W resistor
d. (2) 68k balance resistors
e. (6) diodes - these seem pretty generic and cheap  - anything special i should know?


part II   
f. (5) .1uF 600V blue blob caps new part : Mallory 150S   5%

g. 2 of these caps are on Phase Inverter pins 1,6 plate, along with 2 resistors:
48k - replace these for better matching and low noise,
Question: metal oxide?  metal film?

h. there's also a similar looking but smaller blue blob .1uF 200V (connected to pin 7 / grid of phase   inverter) Can i use another . 1 600V here?

i. (3) .047 600V paktron :   mallory 150s  5%

j. (5 )25uF 25V (white mallory's) replace with sprague atoms
Question: my V5 12AX7 tube also has one of these hanging off pin 3 - what is that needed for?


k. Replace Resistors 470 and 1.5k soldered to 6L6 sockets (in case they're cooked)


part III see what happens next

Any pointers greatly appreciated.

I have plenty of photos, but they are too large at the moment.  attaching some layout/ markups I'm working on
Thanks,
Jeff

[jeff_free69]

circuit board layout ( crudely modified from a standard black face design)  most of the difference is around the phase inverter and bias circuit .  The bias circuit (not shown) is the balance version (but I imagine most around here are well aware of that)

This also shows where the Master Volume  is spliced in  : "MV2" "MV3"

[PRR]

Electrolytics, probably.

Most of the rest: you can do more harm than good by wholesale replacement of random parts. Few of us can make solder joints as good as the workers at Fender did. Especially working inside the box (they had the boards out in the open). You can run the amp without the power tubes and verify smoke and no-load voltages. Many bad parts will be apparent as wrong voltages. 48k where should be 47k is NOT! a problem. (These amps would work with all 20% tolerance, 38k-56k; but good-quality parts in 10%-5% had become too cheap to ignore.)

And yes, do NOT! mod until you fix what's broke and play it a lot. It has been a fine amp for most of 50 years, it is new-to-you, learn what it is as-stock.

[Papa Jim]

I'm no expert but I would blow out the dust and cobwebs, fix any obvious things like unsafe power cord, and that broken cap lead. Then from that point remove all the tubes and treat it like it was a new build by running the input ac cord thru a current limit lightbulb circuit you can build, and before powering up without the tubes, ask on here what to do and check for. You may be getting rid of stuff that might possibly make that a sweet sounding amp even though it is mismatched like tubes and certain parts are original. Original can still be good. Get it working and if it sounds good, play it till it breaks.

Whoops just seen PRR basicly saying some of the same too.

[2deaf]

The '72 Twin Reverb is the best amplifier Fender ever made.  No, really.  I bought one 36 years ago that had a real rough first 11 years.  I didn't take it seriously and I altered it and I've been kicking myself ever since.  I picked up a '73 in Flagstaff, AZ more recently and this time I left it all stock except the 'lytics and the bias current limiting resistor.  I had a directive drawn up to have the amp buried with me when I die.  Not really.

You're kind of new to this forum and I really don't know how familiar you are with these things.  Anybody that posts a question on these forums gets a whole lot of noise.  A lot of that noise is actually useful, but it is such a random dispersion of knowledge that it just confuses people.  Some of it is just plain wrong, adding to the confusion.  So how are you to know?  The number of posts doesn't mean squat.  sluckey is one of the most knowledgable guys when it comes to guitar amps, but his post count on an alternate forum is low and some folks there don't pay the proper attention to him.  pdf64 has a low post count here, but that cat has a vast knowledge.  PRR has a real high post count here and he also has a vast knowledge.  So why should you pay any attention to me?  Frankly, I can't think of any reason to.

If you want to start with the power cord, that's fine.  Note that Fender habitually wired the convenience outlet backwards, so pay attention to the neutral and to the hot.  No need to remove the ground switch, just snip the .047uF capacitor out and leave the switch for cosmetic purposes. 

The doghouse is the next thing that requires attention.  It has already been altered from your description.  Hopefully they only replaced the capacitors because sometimes they feel the need to alter the board.  Some pictures would be really helpful.  You're on Doug's forum and he sells the parts you need, so it would behove you to order them from him.  Besides, he's a really cool guy and his service is excellent.

There is no need for designer products when it comes to filter capacitors.  Use the 100uF/350V Illinois cap's for the two 70/350V cap's.  Use the 22uF/500V Illinois cap's for the three 20uf/500V cap's.  Use the 100uF/100V Nichicon cap's for the two 50uF/70V bias cap's.

Do those things first and report back.  Do not, under any circumstances, alter the main board at this juncture.         

[shooter]

Frankly, I can't think of any reason to.

ah come on, you know there's a perverse enjoyment in being ignored 

[Willabe]

So why should you pay any attention to me?  Frankly, I can't think of any reason to.

I would  certainly, without hesitation,  add 2deaf to the list he guys he mentioned, and off the top of my head, dummyload, Ed C. and tubeswell. There are several others too, that I can't think of right now.  (2deaf is being modest/humble.)

[SILVERGUN]

The '72 Twin Reverb is the best amplifier Fender ever made.  No, really.

jeff_free69....that's a pretty big statement from a guy whose opinions really do matter.

So, 2deaf, does it look like he's got the right schematic for the '72 of which you speak? (I don't see a date on there) I have a special folder on my desktop for "the best" schematics.
I remember when I read PRR referring to the 5F6-A as a perfect amplifier. I immediately started gathering parts.

The beauty of this for you, jeff_free69, is that you stumbled upon 95% of what you need to recreate the "best amplifier Fender ever made". I'm happy for you, 'cause it wouldn't be cheap to try this from scratch. Most guys will never have the chance to hear it for themselves.
Get those pics sized down and let us have a look-see.

[Papa Jim]

Both Willabe and Silvergun are great help too Jeff. Listen to all these guy's and end up with a really great amp.

[2deaf]

So, 2deaf, does it look like he's got the right schematic for the '72 of which you speak?

010182 Rev. C is very similar to how my '72 was originally.  Mine has a 1K bias resistor and the schematic shows 470r.  I have seen others with the 470 and my '73 had a 470 originally.  The cathode of V4 had an 820r resistor on my '72 and the schematic shows 1.2K.  My '73 has a 1.2K resistor just like the schematic. 

[uki]

...
If you want to start with the power cord, that's fine.  Note that Fender habitually wired the convenience outlet backwards, so pay attention to the neutral and to the hot.  No need to remove the ground switch, just snip the .047uF capacitor out and leave the switch for cosmetic purposes. 

...     

@jeff

I dunno how the electric installation in the buildings are  where you live, but down here in more than 95% of the places there is no ground in the wall where we plug the our amps. I did got a shock last gig just about a month ago, from the mic at the amp, was correcting its position in relation to the speaker, I did touch the mic and strings at the same time... TTZZZZZ   didn't hurt just spook the hell out of me(I got that on video, not published), .. gladly I do have the ground switch on the amp, and the 3 wires cord with ground, some places have sockets on the walls with 3 pins connection but no ground wire.

[mresistor]

I recently restored a '72 Twin that didn't have the pull M switch on it.  I replaced all the electrolytic caps in it.  I changed the bias circuit to AB763 specs since we get quads these days that are fairly matched.     The info on how to do it is here   https://el34world.com/charts/bias_conversions.htm   The cabinet on the one I worked on had water damage and was warped. I was lucky to find a Super Twin cab for sale to replace it.
I also replaced the voltage dropping resistors under the cap can along with the caps.   I didn't replace the 220k leveling resistors and Doug mentions that they see little stress. Good luck with your restore project.

[Papa Jim]

Earth to Jeff  Hope you follow these guy's excellent advice.

[jeff_free69]

Wow! thanks for all the replies - I knew I came to the right place!

Just to address some of the many good comments:

Already built the current limiter

and blew out the cobwebs  (original condition of cabinet shown - its pretty shabby) and surface scuzz on all the components (main circuit board shown after cleaning, but the rectifier shot still shows it)

 Mine has a 1K bias resistor ( thats one of very few deviations from the Rev C schematic;  the others are trivial 470 vs 460, 47k vs 48k)
 
I'm pretty experienced with soldering, so not concerned about that when the time comes.   Probably not evident with the downsized photos, but  on Mar 6, "Richard Hand" must have had one biga$$ed soldering iron  - lots of burnt of wire and there's a brown resin residue on every joint. Dunno - maybe thats normal here? 

Powercord - will bypass the ground switch, but leave it in for cosmetics.    My days of lugging this 70 lb beast are over - this baby is staying well grounded in the studio!  (Back in the day, my guitarist had this same amp  - maybe even the same year; my back still aches thinking about it :)

BTW These images turned out to be around 250K , so I can make them larger if need be - lemme know

[jeff_free69]

more small-ified photos

[shooter]

I've got some barn mice that would love that cab 

[Ed_Chambley]

Resin would not be considered normal, at least from the couple hundred of this era I have been into. I know 2deaf and PRR said keep it stock to start. I would too, but I would consider building a new board after you get the amp running.


Here is why. If I plan to play the amp a lot, which a twin if you have the space is my favorite combo amp.
I had not that weighed 87 lbs combo and I was you get too. No casters either baby.


The early 70s were the worst I have run across for the boards to become conductive by taking on humidity. I have head the tone on my 73  Super Reverb change as it warmed up and also the floor noise drop. I made a G10 eyelet boart to match the fish paper board. I normally just use od225 caps and mf resistors leaving the stock board alone. I prefer heaters below, like tweeds but it doesn't matter. Just looks neater.


So eventually I will have replaced most parts, but I also have the opportunity to renew the chassis while it is bare. Any time I have ever tried to keep a player amp with older components I get noise sooner or later and it seems as if I am inside it more than I meet to, which a twin  is a pain to handle even just that huge chassis.


I am sure you will have a fine amp. Just Sharing  some information.

[DummyLoad]

in my collection i have a '67 super reverb that has pops and hiss at random in the reverb circuit for about 10-15 when fired up cold. after it warms up it's fine. when i measured DCV from the board to ground on the amp, i was seeing 40-50VDC. at some point in time in the future, i'm probably going to have to rebuild it. for now, i just let it warm-up before playing through it.

i also have a '75 bassman 100 that had a very rough life and judging from the amount of mildew and rust, seems it was stored long term in a high humidity environment. it wouldn't stop popping, hissing, and crackling at random. measuring from some areas of the board to ground, i was seeing over 100VDC. i gave up and i gutted it. i laid out a modified AB165 circuit on G-10/FR4 board for it. i punched another hole in the chassis for the 4th preamp tube needed. i need to finish assembling it.

the point is, as ed states, is that some fender amps of that era that have had a hard life, may need to be rebuilt to salvage. when you get yours up and running chopstick the board to rule out any bad connections, then measure DCV on random parts board to ground to get an idea of the condition of the board in yours. that said, i have have some fender amps with a conductive board on my bench, that had no noise issues at all.

good luck with yours. twin reverbs are very, very nice sounding amps.



--pete

[Ed_Chambley]

in my collection i have a '67 super reverb that has pops and hiss at random in the reverb circuit for about 10-15 when fired up cold. after it warms up it's fine. when i measured DCV from the board to ground on the amp, i was seeing 40-50VDC. at some point in time in the future, i'm probably going to have to rebuild it. for now, i just let it warm-up before playing through it.

i also have a '75 bassman 100 that had a very rough life and judging from the amount of mildew and rust, seems it was stored long term in a high humidity environment. it wouldn't stop popping, hissing, and crackling at random. measuring from some areas of the board to ground, i was seeing over 100VDC. i gave up and i gutted it. i laid out a modified AB165 circuit on G-10/FR4 board for it. i punched another hole in the chassis for the 4th preamp tube needed. i need to finish assembling it.

the point is, as ed states, is that some fender amps of that era that have had a hard life, may need to be rebuilt to salvage. when you get yours up and running chopstick the board to rule out any bad connections, then measure DCV on random parts board to ground to get an idea of the condition of the board in yours. that said, i have have some fender amps with a conductive board on my bench, that had no noise issues at all.

good luck with yours. twin reverbs are very, very nice sounding amps.



--pete

Yes DL, After trying to read what I wrote early this morning on a damn tablet (PRR I did get a nice USB Keyboard), but when outside at daybreak with my dogs I make a lot of typos.  Yes, I could use spell check, but if I get too perfect I am impossible to live with.


So let me say, yea, what he said.  I will say I had a 65 Deluxe with a conductive board, but this jewel was all stock.  I am not sure any of the larger Silverface amps amps will increase a lot in value since, but I will not drill a hole in one.  It lived it's life in a very humid environment and created a delimma for me.  Well, the amp has to work well.


I did have end up having to remove and replace it.  I did sell it and informed the guy I had replaced the board with one I made, but still had the original board and he was welcome to it, however the one it it had the same parts, brand and year.  I had some of the blue molded caps and Carbon Comp.  The guy actually preferred the amp this way.  He plays at his church and the amp sits there and looks so nice most other players think it is a reissue.


The key on you twin is the master volume and how you like it.  Like I said, I have played a lot of twins, but they do seem strange with preamp distortion.


The first one I ever played was at my local music store.  Found the master, got it distorting an playing Train Kept a Rolling just as you would think a 14 year old would.  I remember it sounding great right before Mr. Attina, the music store owner said turn it off and go home for a week.  I was banned, but it was worth it.

[mresistor]

The cabs from the 70's era were not finger jointed, instead they are rabbet jointed and then glued and stapled. I supposed it was a cost saving measure. What I've seen in many of the larger amps like Supers and Twins is that the glue has let loose and the joints have separated which has required peeling back the tolex to reglue and clamp the joints. The ones with the castors which have the reinforcements in the bottom have shown to be less prone to bottom joints coming loose.  In some cases it seemed only the tolex was keeping the joint together.  Might want to take a look at your cab joints.  Also I tried once to cut out the speaker baffle to build in a "removeable" baffle like the earlier cabs..  it was a disaster. If the cabinet is not so hot, mojo has replacement that is nice.

[nandrewjackson]

I think it's great that this amp was found before hitting a landfill somewhere.  Everyone here has their opinion on how to proceed, me too.


Based on those photos, I would gut all the components and wiring. Total rebuild. 


I'm NOT recommending that YOU do that. That's what I would do.


And that's probably why serendipity dropped the amp into your hands, not mine


LOL


 


Seriously though.  Good luck, take your time, use patience.  This forum is definitely gonna help you through the process. 

[jeff_free69]

I think mechanically the cabinet is fine, so not worried about that.  but the tolex and hardware are grungy.  Oh yeah - the front of the chassis is dented / bent.  won't be surprised if the pots in that area have issues.  yeah this pup has had a hard life....

I can see a complete rebuild may be inevitable.  But at least that's possible (something i never realized).  just hoping the big ticket transformer is good.     

I'm going to start with the basics (Electrolytics, etc)  - putting together my first Hoffman amps order now!
but I'm not seeing anything close to the 70uF 350V filter cap.   Its suggesting a 100uF ,  since thats  50% out of tolerance , how will that affect things?  ( I may have read that can thin bass somehow -  dont quote me)

[sluckey]

It's very common to replace those old 70µF/350V caps with modern 100µF/350V caps. Consider it an upgrade.

[jeff_free69]

It's very common to replace those old 70µF/350V caps with modern 100µF/350V caps. Consider it an upgrade.

Close enough for rock n roll, I always say!

Order is in  - hopefully will have some good news to report by this time next week

[eldredjames]

  I've got to congratulate You on your most serendipitous find.  All I ever spot are pennies.

[jeff_free69]

While I patiently await the arrival of the parts and a fresh roll of Kester, I did a little more cleanup.
I didn't find any actual mice, but it sure did look like it came from a barn.

Its hard to imagine how something could get this greasy and grimey - what were they doing, cooking french fries in there?
Look at that gunk!  On the right is where I already took several passes with windex and a toothbrush etc  (there's still some gumminess there, compare to the shiney, pristine part under the doghouse; only a razor blade got it down to bare metal, but that started to scratch it).
I have no reasonable explanation where it came from...

[Papa Jim]

Maybe try a Scotch-Brite pad with some VM&P Naptha (lighter fluid). Best cleaner ever and doesn't harm parts.

[jeff_free69]

The pad helped a lot, thanks (no sense babying it like it was a silkscreened faceplate).  And a little elbow grease - no need for the naptha ( I don't light that many things on fire anymore)

Hey - the parts order came!  right on time and perfectly filled. 
Time to get serious !

[DummyLoad]

windex contains ammonia & ammonia is VERY corrosive.

use mild soap & water & lots of elbow grease. use alcohol for the tuff stuff. 


--pete

[sluckey]

Mineral spirits cleans a lot of grease and grime. I usually follow with denatured alcohol.

[jeff_free69]

Thanks - good to know  - especially when i get around to the front panel.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

What do you think of my plan of attack for phase 1* ?
(out of an abundance of caution,  basically just make sure the power section is good  for just a few bucks )

Do the Deathcap bypass

Replace Electrolytics
 5 in doghouse
 2 on bias / rectifier board
 
Replace the (2) "dreaded blue" .1uF power tube Grid coupling caps

Replace the diodes

Inspect and resolder anything in need

----------------------
power up  WITHOUT tubes  (note I don't have a variac)

check voltages etc 
(Where?)

Have a glass of wine, assuming there was no "BIG surprise"

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

*taking the lead from this D-lab video (there is also a part 2).

NOTE  I don't think he'e working from the correct schematic.  This twin looks nearly identical to mine but appears to have the push-pull piggybacked on the Master Volume (so its later than my '72).  He checks the bias pot to make sure it works but doesn't seem to take into account that on these later models it was a balance, correct?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
phase 2
replace the (4)   470 ohm screen resistors on the power tubes ( 3 are measuring just under 500 , but one is over 700)
add 1 ohm shunts
Put in tubes
measure bias voltages
?

Any other tips?
Thanks in advance.

[Papa Jim]

Looks like a good plan except I'd have a beer instead of glass of wine. 

[shooter]

check voltages etc  (Where?)

B4 I do this, I OHM the PS, last TAP, should NOT be anything close to zero or low kohms, typical is infinity or really big.

then I ohm EVERY plate to it's tap, (1 lead at tube socket)
then I ohm EVERY cathode to ground
then I scribble the volts I expect from schematics, math, google
then I do the volts

[shooter]

oh, forgot then I smoke my wine 

[uki]

Check out on youtube uncle doug he have lots of very good videos about tube amps!

Several about Fender amps, how tube amps work and so on.

Hint, Use some old teeth brush to clean the new solders, make sure the solder melts and looks shine after done, always clean the iron solder tip for every new solder.

 

[2deaf]

note I don't think he'e working from the correct schematic.  This twin looks nearly identical to mine but appears to have the push-pull piggybacked on the Master Volume (so its later than my '72).  He checks the bias pot to make sure it works but doesn't seem to take into account that on these later models it was a balance, correct?

So you have a pretty good indication that he doesn't know what he is talking about.  The amp he is working on clearly has a balance control, but he thinks that it is a level control.  He only has one 1-ohm cathode resistor, so he doesn't realize that the other pair of output tubes is getting colder while he increases the the current through the tube with the cathode resistor.  May have something to do with the hum.

My personal favorite is the idea that a shorted OT doesn't put a load in series with the tube and the tube will run wild with no load.  He may have topped Uncle Doug with that one.

I figure one of those ugly blue caps must have insulted his mother at some point because he has a completely irrational grudge against them.  He replaced those 0.1uF caps for no reason.  There is a demand for those blue caps, but I doubt he is removing them for resale.

My advice is to delete those videos.  He seems like a pretty good guy, but he has no business posting a how-to video with such a serious lack of knowledge.  Some guy on another forum said that Uncle Doug needs to be teamed up with a fact checker.  Pegged it.

[2deaf]

What do you think of my plan of attack for phase 1* ?
Do the Deathcap bypass
Replace Electrolytics
 5 in doghouse
 2 on bias / rectifier board
Replace the (2) "dreaded blue" .1uF power tube Grid coupling caps
Replace the diodes
Inspect and resolder anything in need
----------------------
power up  WITHOUT tubes  (note I don't have a variac)
check voltages etc 

Once you get the power supply working, you can determine if the 0.1uF PI coupling caps are leaking.  I see no reason to replace them if they aren't leaking DC.  I also see no reason to replace the diodes unless something is found that would indicate replacement.  If you do replace the diodes, make sure to heat-sink them while soldering.

I see in your pictures that the convenience outlet is wired backwards.  Not that big of a deal in light of the incorrect wall outlet wiring found everywhere, but if you replace the cord you may as well wire it correctly. 

[tubeswell]

Good score!

I recently (year before last) scored a 73 Quad Reverb complete chassis that had been dogified by previous owners and put into a shell-of-a head cab. It was badly mauled in fact - took about 40 hours to get it running okay (including output tube socket replacement etc). Your TR looks much more original - good foundation for restoration.

I know one guy who does painstaking restorations of silver face amps, he meticulously dismantles the board completely and scrapes all the excess wax off them (on both sides!) before reassembly. Probably no need to go to those lengths - I didn't with mine.

The filter caps aren't original, so yes - replace all of them, including the caps in the bias supply. As to whether you need to replace the diodes, your call. Test them and if they're all okay, keep them. Test the coupling caps (with no tubes in first) to see if they're leaking DC. If they're okay, leave them alone. Also test the LTP slave triode decoupling cap for DC leakage - a leaky cap here can skew the LTP (and output tube) voltages. Might also pay to disconnect the OT and test that it isn't shorted. Inspect the output tube sockets carefully for signs of fire/arcing, including the screen grid resistors (although from the photo, its hard to see whether there is intact any problem in this regard). Clean the mould off the boards.

Otherwise do the usual new build startup procedure (including running a dimmer bulb when you first power it up to check there is no PT short or other short in the power supply).

[jeff_free69]

Wow lotsa food for thought! 

First and foremost..

Looks like a good plan except I'd have a beer instead of glass of wine. 

Yeah, my first choice too!  Just mimicking Mr D-labs and his  beverage of choice (not that there's anything wrong with that). 

B4 I do this, I OHM the PS, last TAP, should NOT be anything close to zero or low kohms, typical is infinity or really big.
 .... then I ohm EVERY plate to it's tap, (1 lead at tube socket)

OK so check the windings in the PS , but not following exactly (still learning the lingo) -
" last TAP ..."
and "ohm EVERY plate to it's tap ..."

Uncle Doug ... has lots of very good videos about tube amps!   Several about Fender amps, how tube amps work and so on.

.... Some guy on another forum said that Uncle Doug needs to be teamed up with a fact checker.  Pegged it.

Well, if I read it on the internet , I know it must be true! :)

But point taken, like everything else, with a grain of salt.  I've watched at least  a hundred videos by Uncle Doug, D-Labs, Guitologist, Mr Carlson etc.   Some of them more than once.   None may be perfect, but they gave hope that there's enough common knowledge out there to do this.   I just think this stuff is so cool.  After about 6 weeks I'm  just starting to get a feel  about whats right, like  that bias-balance thing.

Once you get the power supply working, you can determine if the 0.1uF PI coupling caps are leaking.  I see no reason to replace them if they aren't leaking DC. 

Test the coupling caps (with no tubes in first) to see if they're leaking DC. If they're okay, leave them alone.

Also test the LTP slave triode decoupling cap for DC leakage - a leaky cap here can skew the LTP (and output tube) voltages.

As to whether you need to replace the diodes, your call. Test them and if they're all okay, keep them.

How do you test caps for Leaking DC ?  I thought you need a special meter for ESR.  Mine is V-O-C-L .

How to test for diodes?  (why not just change out for something that cost 15 cents?)

What is "LTP slave triode " ? 
probably something obvious - I'm just not getting it at the moment . 

Time for a beer - Thanks!

[shooter]

pick ANYTHING, learn "the language" you're golden 
TAP is each "node" for B+, typically you'll see A B C D in a circle or square on a schematic.  preamps have 2-3, so use the one "associated" with that tube

[2deaf]

How do you test caps for Leaking DC ?  I thought you need a special meter for ESR.  Mine is V-O-C-L .

Once you get the power supply going, there should be a high voltage on one side of the 0.1uF caps and zero volts on the other side relative to ground.

[tubeswell]

How do you test caps for Leaking DC ?  I thought you need a special meter for ESR.  Mine is V-O-C-L .

see 2deaf's response

How to test for diodes?  (why not just change out for something that cost 15 cents?)

Use an R-meter with one meter probe at each diode lead (with the amp switched off, discharged and unplugged). Good diodes will measure a resistance one way, by when you switch the probes over to the opposite leads, they will read open connection. Another way is to (carefully) use a scope to check they are rectifying when the amp is powered up.

What is "LTP slave triode " ?

Non-inverting triode

[2deaf]

Well, if I read it on the internet , I know it must be true! :)

But point taken, like everything else, with a grain of salt.  I've watched at least  a hundred videos by Uncle Doug, D-Labs, Guitologist, Mr Carlson etc.   

I don't usually watch those videos and this is the first time I've watched D-Labs videos.  Man they were long.  I must have fallen asleep because I never did see what he did about the hum (60Hz? 120Hz?).  There is a difference between taking a video with a grain of salt and taking what I say with a grain of salt.  There are a whole pack of fact checkers on this forum and they will immediately jump down my throat if I say something that is incorrect.  I ain't complaining, that's the way it should be.  They will frequently say exactly what I said right after I said it like as though I had never said it, so when you see that you can be more confident that what I said is indeed correct.

Enjoy your beer.   

[jeff_free69]

Sorry, not trying to break etiquette or overlook your valid suggestion.

Out of all the videos I watched, the reason I highlighted that one is simple.   Most amp repairs start off with a working amp with some common, known issues (noise, hum , wonky tremolo etc).  So the tech just plugs it in and does his thing.   This one had a major red-plating problem and started with the tubes pulled, which was new to me.   With mine being a giant question mark, it seemed prudent to try that approach, which is why I came here for validation.

While I certainly don't want to spread false or incomplete information, does it not serve a purpose to provide clear commentary and critique to said videos?      I hope anyone seeing the video link also sees the question I raised, and more importantly, the highly informed answers given here.   
BTW I didn't realize the link would pop up as a huge picture here.  No need for both of them - I'll at least delete pt2 for now. 

FWIW - D-labs strikes me as an excellent military electronics tech and a very entertaining guy (reminds me of a cross between Walter White and Ned Flanders).  But he's not a musician and his videos don't end with a money shot (until the latest where he invites a friend over to play).
Uncle Doug goes the extra mile and tries to explain the theory in relatively simple terms, which is helpful.  I'm not smart enough to know where he gets off-course, but its not that crucial.
itSall Good,man!


The beer was good, real good

[jeff_free69]

Tomorrow's looking like a nice rainy day, so perfect  to get this thing going...

In the meantime I just want want to give a shout out to an amazing performer and amp I just saw - Amongst the most gorgeous amps I've ever heard, and never really heard of before  - a Brownface Vibroverb.

The venue was the  Greenwhich House School of Music and the artist is Celisse Henderson.  Her current "regular" job is playing with Trey Anastasio in his new project "Ghosts of the Forest".  She's an amazing singer, performer and talented multi-instrumentalist, in a solo show.

Its an intimate room, holds about 80 people, minimal miking and I sat front and center.

The amp was perfectly punchy, dynamic and expressive.  Seems to be a relatively rare model - Even the reissue is no longer issued.   
Under the glitter I think the guitar was a Jazzmaster.   For this gig most of that hefty pedal board was unused (good call!)

I say a prayer: "Please God, help me make my amp sound as good as this one!"

[jeff_free69]

OK - some decent progress today.  Some good news, some not so good (but maybe its very good news!)

1) Power Cord

I see in your pictures that the convenience outlet is wired backwards.  Not that big of a deal in light of the incorrect wall outlet wiring found everywhere, but if you replace the cord you may as well wire it correctly. 

Good catch!  I wasn't paying much attention to this area, but your are correct.  PLUS while tracing this out I discovered an intermittent fault in the power cord!   The hot had no continuity at all when the cord was twisted a certain way.  Isolated that down to the area where the cord restraint screws into the inside of the cabinet about 10" down (more abuse - somebody must've yanked it good!).    So looks like another part to order.  But I'm thinking that could've been sufficient cause for someone losing interest to just give up.
 
What do you tink about this diagram to rewire the new plug? (with outlet and bypassing ground switch/death cap)


2) Doghouse
moved on and started replacing the filter caps.
I'm including a shot of the starting point showing all the resin/ mystery substance slop.  Trying to clean that up.
It quickly became apparent to me that the best way to do this is to completely remove all the leads in any given eyelet.  Clean them all up and start fresh (as can be). 


3) finally , just looking to get a sanity check (its getting late). 
The last (2) 80uF (now 100 uF) caps on the left have unfamiliar markings.  Before I tack them in - is that the correct orientation?

[Papa Jim]

If the original two were correct then you have those two on the left correct also. Those two just show which end is - instead of showing which end is + like the originals. I would check the polarity probably against the schematic instead of relying on those supposedly originals to be correct. Just me though.

[DummyLoad]

illinois 100uF 350V caps - orientation is correct in the last pic.

about the polarity marks on the illinois caps: the markings on the cap body "> - > - >" the arrows point to the negative lead.


--pete

[jeff_free69]

Thanks! -  For sure the left most one is supposed to be opposite of the rest (they need to be in series , to double the voltage).   
Was trying to remember that arrow thing ("it points how electrons flow from positive to negative").   gimme a break whats so hard about printing  a couple of "+++"?   
Funny thing, now that I look at my photo, I can see its got a dimple at the positive end like the rest.  Totally overlooked that with all the confusing and distracting graphics!  Its easy, once you know...

[Papa Jim]

yeah really. I hate those markings.