Picked up a Silverface Fender Pro Reverb Head in Pieces

[PRR]

We know what resistance is. (If you don't, learn.)

"Impedance" means something extra.

As said, it can be reactance (capacitor, inductor). Now we need to think about Frequency.

It *can* also mean there is a voltage dependent aspect of this "resistance". Consider a Silicon diode. Infinite resistance one way, the other way is 30 ohms at 1mA but 3 Ohms at 10mA. It's a very "bent" resistor. It's bentness depends on voltage or current, but not (much) on Frequency.

But Audio usually means wide-band, in both frequency and voltage. Usually stuff acts "the same" for 100Hz to 10KHz and 0.0001V to 100V. When it doesn't, usually we "want it that way". Tone-controls bite highs more than lows. Speaker impedance is all over the place but we usually pretend they are a "resistor" because the deviations have been allowed-for by the speaker designer.

[Platefire]

On the pro reverb I drilled holes for the OT and also drilled out the wiring access holes larger and installed new grommits. I didn't install the OT though, the thing is so heavy I'll wait and put it on last thing to make handling the chassis easier while doing the final wiring. Got a parts order in with Doug. As soon as I get those in I can do the final wiring, install OT and fire it up and see where I'm at with this amp.

On the impedance study, Thanks! My brain is reelen from the influx of info, may take me some time to digest. Plate

[thermion]

Archive this please!! Very nice insight gents!

[Platefire]

Got parts in for this one today from Doug and couldn't wait to put them in. I installed all AA165. I fired it up about 3:00 PM on my light bulb limiter and no smoke so I went whole hog 120V. It started squealing like a pig right off the bat so I had to switch 6L6 plate leads--that did it. Both channels working pretty lively. No reverb or trem. Don't know if this is one that has to have trem switch plugged in to activate? Also don't know it the reverb tank that came with this one is good or not--it may be the tank is bad. I haven't installed any 1 ohm resistors on the 6L6's cathodes yet---just set the bias -51 like schematic and power tubes seemed happy. I got a 5U4 rectifier in there, don't have a GZ34. The thing was running pretty quiet. Some voltage readings are:

V1=239,230(normal chan)

V2=244, 268(rev chan)

V3=405(rev driver)

V4=273, 262 (rev recovery)

V5=215, 435 (trem)

V6=234,233 (PI)

V7/8=Plates-436/439, Screens=433/435

Forgot to check heater voltage

Platefire  

[eleventeen]

I guess the good news is that you are running with that skungy old parts board, yes? Congrats!

[Platefire]

Yep! At first I thought the hacker hadn't messed with the board very much but I was wrong. They had disconnected stuff, changed values, terrible soldering, caps added in strange places and extra pots. Apparently they had been reading about a lot of mods that could be done to this amp but didn't have the where-for-all to carry them all out. The only mod I can see that was done successfully was converting the bias from balance control to bias control--like the AA165. Fortunatly I had most of the stuff I needed in stock. It's all AA165 except for one thing they did I kind of like and will wait on changing out---the ground wire for the reverb control pot terminal runs to the gound terminal of the rev chan vol ground terminal--when you turn up the reverb in adds gain(like crazy) that really makes a nice feel/tone. Of course it also adds reverb but it sound so good you hardly don't mind. Anyway I'll play with it until I decide if it's useful or not:>/

BTW-fixed the reverb and Vibrato---reverb tank had a ground wire from the output transformer that had fell off the rca jack and just soldered that back. The vib had one leg of the opto eye disconnected that may have been one of their gain mods, that I resoldered back. Plugged in my vib pedal from my Silvertone 1482 and it switches it very well.

I added the 1 ohm resistors to grounds on the 6L6 cathodes. Got an old set of tubes in there kind of unbalanced running one at 33ma, the other at 24ma and bias voltage about -49.

Gosh!! The thing is sounding good to me. The tone stack is kinda weird but I'm learning to work it.
The responsive feel is impressive. It's fender sound but a little different. Platefire  

[eleventeen]

At the risk of stating the obvious, having a parts board with the terminals laid out in a way that suggests the component layout is powerful juju. Compared to building on a generic turret board where all the terminals are equally spaced; and only at the edges... with no terminals part-way across the board ..it's a major difference. Even if you are changing a silverface amp to a blackface one. (I don't know offhand if there are differences in the black/silver parts boards, but they are certainly very minor) The proprietary layout lets you see mods and changes very easily.

[Platefire]

Well I guess I should have clarified all the pre-existing mods wasn't all on the board--some on the chassis and some on the tube sockets. A duel one meg MV pot in the vib intensity pot hole, a 250K
midi pot in the rear vib rca jack footswitch hole, several caps on preamp tubes sockets between pins--I snipped off. On the board it was mostly cathode resistors and bypass caps of different values than stock. Also removed a terminal strip where they apparently used to wire the duel MV up. Most of the wiring to hook up these mods was either never installed or removed, so you could only guess to what they was doing.

I just wanting to bring it back to a stock fender circuit, and to my understanding AA165 was the new circuit revised from the non-reverb Pro AB763 to add reverb. I think this amp might have originally had the aa1069 circuit but not sure? It's kind of nice to have an old kinda vinage(73) fender of my own. Ever since I started working on tube amps I've had my eye out for an old fender to fix up and well here it is. Platerfire

[Platefire]

My bias supply has a pot as in the AA1069 schematic which I think may be a bias balance control.
The previous owner converted that same pot to a general bias supply like on the AA165/Ab763. It works pretty good but in turning the setting clockwise I run out of movement before I reach my desired bias setting. Topped out I can only get 31Ma where I would like to get 35 to 40 on the 6L6's. As I remember this can be adjusted by changing the resistor value on the pot to ground that is presently 27K-----do I need to go with a lower value resistor? I've adjusted these years ago but forgot what I did.

The Vibrato seems kind of weak. On the speed it adjust the speed pretty well to about 50% on the pot then seems just to loose it's effect into nothingness. Also on the intensity, it don't seem to provide the depth I'm use to on my other amp vibratos. What can be done to make it stronger?

Thanks, Platefire

[sluckey]

do I need to go with a lower value resistor?

yes

What can be done to make it stronger?

replace the roach

[Platefire]

OK, Thanks sluckey

Yeah they got two 50K paralled for 27K. Guess I'll start with a 22K then 15K or 10K as  needed.

On the existing roach, it went south on last amp fire up. When you hit a note with any kind of authority
the vib photo light goes out and you just get static. Light stroke and it blinks off and on but weak. Platefire

[sluckey]

On the existing roach, it went south on last amp fire up. When you hit a note with any kind of authority
the vib photo light goes out and you just get static. Light stroke and it blinks off and on but weak. Platefire

Say what? The blinky neon light in the roach is totally independent of playing notes. Unless something is wired wrong or the board is conductive.

[Toxophilite]

Nice job so far
I'm certainly envious..in a nice way!
I want one too!

[Platefire]

Sluckey, thanks for coming back an indicating that appeared to be a ground out problem on the roach. I went back and did some more checking--no continuity between board and eyelets at roach, checked continuity between roach leads and connecting components---good, and then I checked the vib footswich connection---ah ha! On the Silvertone 1482 footswitch I am using I had to use a 1/4 to RCA adapter and the adapter was grounding out. So after correcting that it is working normally again but still weak. I like to get a "Crimson and Clover" type of wave even though I may never use it but can't get close with this--very undefined. So I'm probably still up for a new roach. Platefire

Toxophilite

Thanks. Got some new pictures I haven't posted yet since I reworked it. I will soon! Think it looks a little healthier how--but regarding looking for these things is very hard in my area. Of course you can buy them all day long off e-bay if your willing to pay the price! I've been checking flea markets, pawn shops, antique shops, garage sales and even tried to get folks I know of that has old fenders in their closets doing nothing to sell with no success until now--14 years. I'm amazed that all the deals some folks on this forum turn up contiually. Hang in there and be patent and sooner or latter you'll snag one. I'm living proof       Platefire

[Platefire]

Somehow it's hard for me to think of this 1973 amp as vintage because to me 1973 don't seem that long ago but gosh!!! Thats been 40 Years   I really think of vintage as 50's or 60's.

Here are some shots of my test and tweak set up. On an amp like this I just live with it a while--test and tweak until I'm satified. This chassis still looks pretty rough especially on the face plate--I'm just going to call it "Road Worn" since that is popular now days. Platefire

BTW-In case someone wonders about those large red resistors on the board that looks like caps, those are NOS resistors I bought at a flea market that are probably vintage 50's at least but they are spot on accurate. If they say 100K they usually measure 100K and I use them when I haven't got a more modern one in stock.

[eleventeen]

It won't win any awards for prettiness, but I am glad you were able to get the old parts board crankin'.

The money you saved on a new board---if you can buy a set of blackface faceplates I predict you will make yourself very happy. It'll make you smile every time you look at it. At least the front, the back is passable.

[Platefire]

eleventeen

I read your post early this morning and really did give it some serious consideration. I finally decided I really like the  personality of that old beat up face plate. First thing people think when they see that is,
"What in the world happened to that"? I like the mystery of what it went through to get where its at. On the other hand the blackface faceplate is still something I could do in the future.

Last night I changed the resistor on the bias pot from 27K to 22K and got some more ajustment leverage with my bias. Probably 20K would even be getter but with the 22 I was able to get the bias right in the middle like I like it--not to cold, not to hot, just right! That sure made a difference. It's sounding like a true USA Fender now. Tried several sets of used 6L6's in it. Tried a set of Svetlana's that came with the amp the are pretty well matched but I just didn't like the sound. I've was running a set of Sovtek 6L6GB's that sound pretty good but are way off from each other. I ended up leaving a set of Sovtek 5881/6L6WGC that sound real good to my ears and are more closely matched.

I worked on the headcab today to glued some of the loose snake tolex back down. Also had to remove the existing plywood & cardboard bottom plate off the reverb tank and install a thinner piece of mounting cardboard on the bottom because the clearance between the bottom of the OT and bottom of cab is so tight. Since the amp is working well, I decided to go ahead and mount the chassis and put it all back together. I ended up with only about a 1/4" clearance between the bottom of OT and top of reverb tank, but I got it in there. A Pro Reverb shall have a working Reverb

After I got it all back together everythng was working sounding great and then my Vibroto started ticking--should have known not to put it back together to quickly   This head is reminding me of my first early 70's Silverface Fender Bandmaster head. My first great sounding amp. Even has the same teal stipe around the faceplate. Bet it even had close to the same circuit before I blackfaced it. I'm just real happy with the way it's sounding and responding especially since I got it biased up. Platefire  

[sluckey]

Ticking vibrato??? Here are a couple tips that may help...

Click on this link and look at the second photo...
http://timeelect.com/jbl-twin.htm

Attached is a Fender Service Bulletin that deals with ticking vibrato...

[SoundmasterG]

For your vibrato, replacing the roach is likely the best way to go. Sometimes the trem can be weak because too much outside light gets into the sensing part of the roach and taping it up can help. They are very delicate and easily broken though and many times if you try to take it off the board so you can tape it up you'll break something! Also, if you want a slower speed, change one of the 0.01uF caps in the feedback part of the trem circuit to a 0.02uF...ceramic is just fine. A lot of Silvertones like a 1484 or 1485 have roach trem that has more intensity than the Fenders, and this is because Silvertone brought it in after one gain stage whereas Fender mixes it in after two.

Greg

[Platefire]

sluckey

Thanks a bunch! That something I'll have to address when I go back in. Should have known better to button it up this soon. I was just really anxious about putting it back together to see how it all fits because I got it in parts all torn down. Thankfully all the parts were there and wasn't lost. Once I got the tolex loose ends glued back down, it went together really well. I use vibroto quiet a bit, so I want to get it up to snuff. I went to the site you had liked and copied the pix showing the new cap .01 Mylar and the lifted roach leads and put it in my Pro computer file.

Greg

Thanks for the tips. I did notice that the light seems to be almost poking out one end of the roach covering. I tried very lightly to get the boot covering to slide down a little to better cover the light up but it didn't budge and I was afraid to use too much force, because like you say, it does look delicate. The roaches are not that expensive, so I may just go ahead a pick one up for next maintainance cycle:>)

Platefire

[PRR]

> I really like the  personality of that old beat up face plate.

The original James Bond car had flippable license plates to confuse people on his tail. (As if the DB-5 was so common there would be two on the same road; might work on my Honda sedan today).



Pivot on each side, spanking-new faceplate to barn-find faceplate at the push of a secret button. (Or just flip it with your finger.) Since the pots/knobs get in the way, duplicate them; now you can have two different sounds pre-set at a flip.

Yeah, I can't even keep my gate-latch working so I shouldn't be suggesting secret-agent mechanisms.

[Willabe]

 

[Platefire]

PRR

Well I've heard of a blackface, brownface and silverface but never heard of a two faced amp  
Really from a distance you can't really tell the face plate is so marred, just on close inspection.

Played the Pro in my church band today. The thing is loud and clean. I started off on 2 and eventually got up to 3. It was nice and quiet with very minimuma operating noise. It took my pedals very well. The amp can do the surf tones very well the long delay 3 spring reverb. The snake skin covering did raise some eyebrows but the drummer liked it. You know how them drummers are  

Platefire

[Platefire]

Got a general question about preamp tube shield/covers. I put the preamp tube tube sheilds back on when I was putting the amp back together and could swear it effected the tone in a negative way where I ended up pulling them back off.

I was just wondering if anyone had any similar experiances. Is this just a figment of my imagination or is there something to it? Platefire

[sluckey]

I'm thinking it's just a figment.

[Platefire]

Yeah, could be. I do know when your tweaking and testing an amp your super sensitive about every little thing. I did do a search and found this discussion. Plate

http://www.thegearpage.net/board/archive/index.php/t-859318.html

[Platefire]

The Snake Head Pro had been doing so good and last night I lost volume in the reverb channel. You can still hear the guitar at a very low volume. I checked the normal channel and it's fully up to speed--so it's not the power amp. I did try another good 12AX7 today in V2 but with no change.  Anything else I need to try before pulling the chassis? Platefire

[sluckey]

V4

[Platefire]

sluckey

Man! I'm so glad for your "V4" post. That was it  

Thanks so much for calling that to my attention--I had missed that gain stage. Glad to have the Snake Head Pro up and running again. Platefire

[Platefire]

When I got this amp up and running I took voltage measurements and biased it and everything was in reason except for V5 Vibrato tube =V5 plate #6 that directly connects to the vib roach. The schematic shows 360VDC there but my reading was 435. Also on V5 Plate #1, schematic voltage says 280 but I got a low reading of 215.

I did measure the Ohms of the 100K resistor to roach in place and it read right at a 100K and also read the 10M R in place to pin #6 plate that read close to 10M. So I was kind of puzzled at what was causing the voltage to be 75 volts above what it should be? As I recall I checked for leaking caps also but didn't detect any. The voltage from  B location power rail measured 436 and schematic reads 440. The 435 reading at roach is almost identical to the 436 B location power rail reading which makes me think it would have to be the 10M or 100K has drifted even though it reads correct in place. Never done much trouble shooting to a vib--so my solution would be to change out the roach along with those resistors and see where it stands. Platefire 

[sluckey]

You will get different voltage readings depending on the VIB footswitch. If switched off or unplugged the voltage at pin 6 would be about the same as the B+ feeding the circuit.

[Platefire]

Well Thanks sluckey

Next time I open it up and check it, I will make sure I do my reading with it engaged. Planning a future maintenance run where I hope to tie up all the loose ends--new roach, new reverb chan #1 input jack, new set of 6L6GC's & bias job--the list is growing. Platefire 

[Platefire]

Here are the finish pictures of my Snake Head Pro.  I may install some hooks to wrap the power cord on and maybe build a cover for it. It could use a back-plate also, so maybe this isn't the final chapter. Platefire

[Platefire]

Got a question? The Pro head makes a ton of spring clash/rattle noise driving down the road unless your on a perfectly smooth road---and those don't hardly exist anymore. So could you stick a piece of foam rubber
under the springs in the tank to help this without effecting the reverb operation. Or what is the best way to address this?? Thanks Platefire

[sluckey]

New shocks.   

[Platefire]

Har! The car is just one year old    Should I trade it in and try another? I could take the head along for the test ride to see how it does. That way I could be sure not to buy another reverb rattling car. Surely there is a better solution than this 

[sluckey]

If you have room try mounting it on the front panel. Might make a difference. Or put the tank in a bag. Or turn the head over on it's back or face down. Or haul it in the trunk. Or get a tank with a locking device. There may not be a cure.

[Platefire]

The height of this head is to low to mount it on the front panel, turning it over is worth a try and I have a SUV so the truck is the same as the drivers compartment. A bag may be a possibility but the clearance under PT is less than 1/4" which may would put it in contact with PT which may not be good. Not important enough to me to buy a new tank. I hauled plenty of reverb equipped amps before but this one in more noisy than normal. I'm not on the road any more and most of my hauling will be between the house and the church ten miles away. So I will probably grin and bare it with no more hauling that I will be doing.

I still wonder about the foam rubber. Most tanks come shipped with foam rubber around the springs that is to be removed upon installation but the reverb tank is an electronic device. Why does the springs have to be free moving to still perform their duty. The foam rubber is non conductive---so how would that effect the sound leaving some in there to restrict movement? Don't the electronic signal traveling through the spring create the reverb and why would impeding spring movement restrict this. I'm sure there is a good reason but I'm not getting it---unless the foam held moisture and became conductive--that would be a problem. Platefire

[sluckey]

Why does the springs have to be free moving to still perform their duty. The foam rubber is non conductive---so how would that effect the sound leaving some in there to restrict movement? Don't the electronic signal traveling through the spring create the reverb and why would impeding spring movement restrict this. I'm sure there is a good reason but I'm not getting it

The 'signal' moving down the actual springs is not an electrical signal. The input transducer converts the electrical signal from the reverb transformer into a 'MECHANICAL' signal that causes the spring to vibrate as it travels to the other end. At the other end, another transducer acts as a pickup to convert the mechanical signal back to an electrical signal to be passed on to the recovery tube circuit. If you inhibit the movement of the springs you will severely impact the reverb sound, maybe even kill it completely. Give it a try.

The foam rubber pad was put in the tank to prevent the springs from vibrating excessively due to shock during shipping. Excessive vibration could damage the fragile transducers. If you really want a good solution replace the tank with one that has a locking device (like the one I showed you). That locking device was designed to prevent excessive vibration during transportation. It has a red warning label to remind the user to 'unlock' it for normal operation.

Tolerance is the cheap solution.

[Platefire]

OK, I didn't realize the significance of the picture---I thought you was just showing me top mounted reverb, I didn't realize it was locking. I've always heard about a locking unit but never seen one. I was trying to see the lever/switch that you flip to lock it but didn't see anything that looked like a lever or switch. Guess they more expensive than a regular tank? Platefire

[Platefire]

Well it's time to go back in. The #1 input jack for reverb channel broke. I ordered another vibrato roach to install while I'm in there. Trying to decide rather to install it normal first and see how it works first or install the mod sluckey pointed out on an earlier post. Platefire

[Platefire]

And I thought installing a silly input jack would be a simple task--WRONG! I've never wired a pair of input jacks like on this AA165 schematic and trying to read the layout and schematic correctly but apparently I'm not following it right. I've done spent several hours on it. The way I had it wired up the first time I had run away gain and after cutting the connection wire from input jack #1 hot term to input jack #2 switch term, input jack #1 started working right with normal gain.

So am I reading it right input jack #1 has the normal 1 meg ground to hot term but what is unusual and is not working for me is the connection from #1 jack hot term to #2 jack switch term. Is that right? or am I reading it wrong?

Right now I have input jack #2 disconnected from connections to input jack #2 as it shows on schematic until I can figure it out. Might be easier just to put a separate 1 meg R on input jack #2. Sure could use some help on this because I did want to wire it up like original. Schematic/layout attached. Thanks, Platefire

[sluckey]

Look at the input jacks on the other channel. Wire it the same. Or look in the Library. Doug has a very clear picture showing how to wire input jacks.

http://el34world.com/charts/CommonHookups.htm

[Platefire]

Thanks sluckey

I finally got it hooked up right where everything sounds right---I think? Guess I had never actually wired up an old fender double input channel before. Never knew it was hooked up like that. kind of mind boggeling at first. Well actually still got it hooked up wrong with the schematic in that I got the 1 meg ground to grid going to jack #2 from the #1 Jack switch term(instead of the hot term). Don't know exactly what that will do but when I plug into each jack separately--seems to be working fine that way. Platefire  

[sluckey]

Look at page 6 of this pdf...

     http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf

[Platefire]

Thanks Sluckey, I will study it. I did go back and try to re-wire it correctly but it only got worst and started the high gain thing again. Best I can tell I had it wired up correct this last time and it still wasn't right. I am going to go ahead and replace the other jack also so I can be sure it's not a faulty jack. Another thing I can't understand is checking grid Ohms through the hi jack it's not dividing the Ohms down to 33K to the tube like it should be, still reading 68K. How can something so simple turn in such a monster? Got to let it go for now. Platefire

[Platefire]

Has anybody got any ideas in the hookup of inputs jacks would cause your gain to be out of control to where by the time you turn up to 2 or 3 volume the amp completely distorted. I never encountered this problem before and it's kind of strange to me as related to input jacks. Will losing ground connection cause this or what is happening here????

I keep wondering if this is related to my input jack installation or something else, but it didn't start until I installed this new #1 jack on the reverb/vibroto channel. I would like to understand, if possible, what's causing this gain problem before I install a new #2 jack because if I install that and it's hooked up like the schematic shows--and its still doing that---I don't know. Very frustrating. Platefire

[sluckey]

I suspect the jacks are not wired correctly.

[Platefire]

Hope it's simple as that. I will rewire in a new #2 jack and see what happens. What it appears to me #1 jack is wired like any standard fender jack, 1 meg hot to ground and ground to switch. Jack #2 had jack #1 hot wired to 2's switch. Both jack #1 & #2 hot is wired to grid through their own 68K resistors to tube. If I got it wrong please let me know. Platefire

[Platefire]

Installed a new #2 jack hooked up like the schematic. Still run away gain! I went over and over my hookup of both jacks and could find no problem. I began to go over the lead dress several time separating wires because I had decided the problem wasn't in the jacks. After going over the lead dress re-arranging wiring for about the third time---bingo--run away gain gone! I still don't know what was causing it but for right now it's gone and amp is performing right.

Next thing is to install new roach, but not tonight. I've had enough for now. Platefire