Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on February 04, 2023, 10:20:07 pm
-
I just completed replacing all the coupling caps and various resistors. The amp is now dead silent as far as operating noise and the tone sounds better than ever. Only problem is when i hammer down on the bass notes especially openE and A I get this rattling distorted side effect.
The weird thing is it only happens with the reverb on. With the reverb off, I get none of that, crystal clear bass notes.The reverb sounds good to. I've double checked the reverb circuit and can't find anything out of order. The reverb tank is Accutronics 9AB3C1B, 3 springs, Long Delay.
So before I discovered it only did that with the reverb on, i tried different tubes, cleaned reverb connectors, checked bias, different Speaker cab, another guitar and cable.
So once I realized it only rattled with reverb on I tried hooking up the reverb from my Allen Accomplice(Deluxe Reverb Clone) to it but it wouldn't work with the Pro??? Seemed like it should work, but didn't.I tried another set of RCA reverb cables and still the same. No doubt, the amp sounds its Fendery tone best through the reverb circuit. So any Light you can shed on this is appreciated. Platefire
-
So you tried swapping the reverb tubes?
-
Yelp, tried swapping different reverb tubes several times. I'm telling you the amp sounds awesome but it's just when you attack those lower notes with authority the rattle shows up.
-
Did you do your filter caps as well?
-
No----but wouldn't it be making some noise if they were bad :w2: When I got it in 2013 it had what looked like brand new Sqrague Atom Filter Caps so I guess I'm thinking that they are still ok. On the other hand, if I can't find
this gremlin, I might have to change them to fine out if that was it!
-
Ok, I hooked the reverb tank from my Peavey Pacer/Deluxe reverb conversion to the Pro and it worked. Did the same old thing when cranked! So it's not a problem with the reverb tank.
Since It don't make the rattle with reverb dialed down to "0", I would think that it's not the filter caps, but in the reverb circuit alone. It don't rattle in the normal channel when cranked and hammering.
However, when I tear it back down to go back over the reverb circuit, it wouldn't hurt nothing but my pocketbook to have a set of filter caps in hand to take care of that too. Those filter caps are 10+ years old.
So I'm looking at them and wondering if Doug's F&T 100uf/350V would work for those pre-standby switch caps instead of the original 70uf/350V ones? I know the 22uF/450 will be fine for the other 3. Platefire
-
So I'm looking at them and wondering if Doug's F&T 100uf/350V would work for those pre-standby switch caps instead of the original 70uf/350V ones?
They will work just fine.
-
No----but wouldn't it be making some noise if they were bad :w2: When I got it in 2013 it had what looked like brand new Sqrague Atom Filter Caps so I guess I'm thinking that they are still ok. On the other hand, if I can't find
this gremlin, I might have to change them to fine out if that was it!
The only reason I mentioned it is because it seems like you can get some funny distortion at low frequencies when the b+ is starving for power. And in your circuit, one side of the reverb runs off of the preamp node, while the other runs off of the screen node. So perhaps something you wouldn't hear on the normal channel would rear it's head when coming through reverb... Just a thought. Another thing to consider may be the bypass caps on the reverb channel. I kinda figure that any electrolytic should be suspect, especially when you've already rebuilt the rest of the circuit.
-
So I'm looking at them and wondering if Doug's F&T 100uf/350V would work for those pre-standby switch caps instead of the original 70uf/350V ones?
They will work just fine.
What about the doghouse? at 1" diameter is cutting it pretty close
-
Picky, picky!
-
Well it's been a while since I re-capped a Dog House. As I remember it had an insulated pad in there between the top of the caps and the chassis---I think? I think the size of the DH is 7 1/8"x 3"x 1 1/4". Length and width is ok, depth is getting close :think1:
-
I think the middle number is 3 1/2 (width)
-
sluckey
Since I will be going back into subject amp for filter caps and what ever it takes to get it up to par.
I was just wondering what adjustment I need to do to my TON circuit to get just a little more intensity?
-
I'm surprised you don't have enough trem. Change tube. Maybe try a 250K intensity pot. Maybe replacing filter caps will help. :dontknow:
-
Really I got enough intensity if I turn it to 10. I prefer to have a little over indulgence room but we'll just see what the new filter caps do. At any rate I am getting it to do what I want even now
It's a WIN WIN :happy1:
-
sluckey
Finally got those new filter caps in, no change. That was last night and since I tested it and realized it was still doing the same thing, I've tried everything I know of to do still with no change :BangHead:
-
Can you plug into another speaker cab?
-
Yes I've done that a couple of times. Tried different pre-tubes several times and several sets ofpower tubes and re-biased them and tried hotter bias, no change. Jumpered in another bias cap.Checked complete circuit with schematic plus voltages. Couldn't find nothing off with that. I've done continuity checks for grounds and connections between components.
It does sound like a busted speaker especially when you hit a power cord on open E. On the higher notes it is like a clean sound with grit.
It seems the reverb circuit accentuates it. I've checked the reverb circuit backwards and forwards but haven't found nothing I could identify. Could the reverb transformer be going bad, but notquit yet? I tried another reverb pan from my Peavey/Deluxe reverb and did the same thing.What ever it is, it's very elusive
I also wondered it that old board that I re-used could be conducting between connections. I've checked that with my MM on continuity between connections but didn't detect any. So I've definitely run out of tricks that I can think of :dontknow:
Edit: Let me add this. I just played in the normal channel
with a delay hooked up. Everything sounds right and normal. Went to the Reverb Channel, used the delay with the reverb knob turn all the way down. Sounds completely
normal. The problem is in the reverb circuit I believe!
-
Have you checked for a leaky cap on either triode in V4?
-
Yes, checked those caps on V4. I just replaced them with new about two weeks ago. Thanks, Platefire
-
More Info: I can turn the reverb knob all the way down or either turn the reverb off with the switch which eliminates the rattling gritty sound. Have tried another tank which resulted in the same sound.
V3 Voltages:
Into Rev Tran=445(Sch 440), out of Rev Tran to V3 a & b coupled plates=437(Sch 430),
Voltage to V4 Plate Resistors=387(Sch 390), Plate Voltage V4a 254(Sch 260), V4b=357(Sch 360)
BTW-I'm using a 5U4 Rectifier instead of the GZ34 on the schematic. My PT has 3A heater current, so if I understand correctly, that will work.
-
It couldn't be a weak solder connection maybe? Have you done anything in the reverb circuit?
-
Well I bought this amp in pieces in a couple of card board boxes. A 1974 Pro Rev, a AA1069. Also who ever had it before me hacked it the circuit with all kinds of mods it looked like they never completed. It's a combo someone cut down to a head. So yeah, I rewired it to AA165 BLackface in 2016. I rebuilt it just enough to get it working back then leaving a lot of old caps and resistors. The amp worked OK but the reverb control has always worked like a gain control. The reverb gets deeper when you turn it up but also adds gain and volume.
So the reverb circuit got new cathode by pass caps and resistors new from 2016. And presently I've been replacing most of the coupling caps and Filter caps. Trying to get it to operate a 100% like it should. So the amp is presently operating quiet as a mouse. Two things that bother me now:
1-Turning the reverb up continues to distort the sound. Turn the reverb off and the sound is pretty close to what it should be.
2-The Overall volume don't seem as loud as I would think it should be. I once owned an early 70's Bandmaster which I would think would be close to what this Pro circuit is. On the Bandmaster the volume was pretty loud on "3". I have to turn this Pro up to about 6 to get the same response and volume.
Other than that everthing is fine :laugh:
-
I've been studying the reverb situation trying figure out what's going on here and one big question I have is what is the main purpose of the 10pF and 3.3M resistor in parallel separating the send and return grid of the reverb circuit.
My guess is that it lets the Vibrator channel use V4b have another gain stage when the reverb is turned off than the normal channel before going to PI. I have noticed that the Vib channel seems stronger than the Norm channel when the reverb is turned off. So it would also be boosting the reverb recovery stage when reverb is on. So this resistor/cap network would let this gain stage serve a dual purpose????
My concern is I have been trying to read the 10pF to determine what's actually in there. This is a DC voltage free grid area, so no way to tell if its doing it's job as far as blocking DC. I have been trying to read the value to make sure the right value is in there with my MM but not getting any reading that makes sense to me like---100nF which is converted to a 100000 pF???
So what I'm getting at is if this cap is bad could it do what I'm experiencing? Everything else seems to check out. Platefire
-
The 3.3M is one of the mixing resistors used to combine the huge dry signal with the weak wet reverb signal coming from the reverb pot via the other mixing resistor (470K). At the junction of these two resistors the wet and dry signals are combined together to be sent to V4A gain stage.
The fact that the dry signal is so much larger than the wet signal means that the amplitude of the dry signal must be dropped considerably, otherwise it would overpower the much weaker wet signal and you would have very little reverb effect. That 3.3M works with that 220K resistor to form a voltage divider that knocks the dry signal down by a factor of 3.3M/220K=15. The 10pF cap is a "bright" cap that preserves that bright fender sound. Without that 10pF the amp would lose some of the highs. I doubt my ears could tell the difference. The 10pF does not block any dc because there is no dc present on the cap. DC blocking is performed by the .02 coupling cap just prior to the 3.3M||10pf.
Your MM cannot measure capacitance smaller than some value. Consult your user manual to see what the capacitance range is for your manual. My Fluke can only measure capacitance down to about 500pF.
That 10pF cap is in the signal path even when reverb is off. I don't think this is the rabbit you are chasing.
-
OK, the 10 pF is not the rabbit! Thanks so much for the explanation, boy did I ever havethat wrong. I never even considered the amplitude of the two signals and the need to reducethe dry signal way down.
Your explanation of how the mixing network works has raised another question which will show my lack of understanding but that's ok. When I look at the schematic showing the dry signals path from V2. One to the reverb circuit and the other to the mixing network. It seems to me that when the dry signal encountered the 3.3 M resistance it would force most of the dry signal through the 10pF as the path of least resistance and not reduce the amplitude at all. Please tell me what my wrong understanding is. Thanks, Platefire
-
> It seems to me that when the dry signal encountered the 3.3 M resistance it would force most of the dry signal through the 10pF as the path of least resistance and not reduce the amplitude at all.
Impedance of 10pFd is greater than 3Meg up to 5kHz.
So 98% of what young folk hear, and 99.9% of what old guys hear, has to come through the 3meg.
-
The 10pF cap looks like a resistance to the ac guitar signal. The resistance is actually called reactance. The reactance (in ohms) is inversely propartional to the frequency involved. This means for low frequencies the reactance is high and for higher frequencies, the reactance is lower. A 10pF cap would look like a 160MΩ resistor to a 100Hz signal, or 16MΩ to a 1000Hz signal, or 1.6MΩ to a 10KHz signal. You can see that the higher frequencies will pass through the 10pF with less attenuation but the low frequencies will prefer to pass through the relatively smaller 3.3M resistor. Make sense? It's no different than the bright cap on a volume control.
Look at this page for a better understanding of where my numbers came from...
https://www.electronics-tutorials.ws/filter/filter_1.html
-
sluckey -Well that opens up a whole new way of looking at capacitors, Capacitive Reactance. I read over the tutorial and tried some of the formulas. I came up with the same answers as they did, just couldn't get my decimals to land in the right place. I've always read about different value caps letting certain frequencies pass and blocks others but I never thought of it as a Reactance/Resistance(based on frequency) that would work in the same way a resistor would. Yes it makes sense to me. Thanks for answering my question!
I looked at my Fluke 115 manual and it says on Capacitance Range 1000nF, 10uF, 100uF, 9999uF. A little hard to understand the way they got it written to me
PRR-I got you on the HF hearing loss---Huh? 3m all the way
-
I have a Fluke 115 and it's struggling to measure anything lower than 1nF.
/Max
-
Yeah I'm beginning to wonder about my 115. Sometimes it struggles to read resistors. I love the Automatic feature on Ohms reading when it's working but sometimes it can't seem to find its way, so I switch over to manual in the K Ohm range on a known ____K resistor and it won't even give me a reading. Somethings either broke or I'm doing something wrong? I may need to re-read my manual again.
-
I snagged one of these and I never take it off of the capacitance setting. It comes with some 3" long clip leads (so as not to add much capacitance) and I've successfully measured down to 10pf.It works pretty good for as cheap as it is. I use it mostly to double check cap values as I'm building.https://www.newark.com/tenma/72-8150/capacitance-meter-with-resistance/dp/41M0998
-
WOW, I like the price!!!
-
I bought this Proster (https://www.amazon.com/Proster-Multimeter-Capacitance-Resistance-Inductance/dp/B071WNNYQT/) last February. Only got about 45 minutes on the battery. :icon_biggrin:
Don't know how I managed a 50 year electronics career without needing to check the value of a cap or inductor. :l2:
-
Man, I didn't know you had a career in Electronics. What did you end up specializing in?
On the Proster, another good price. Did they have any analog meters 50 years ago to read capacitance? All I ever knew about is those old analog MM--Ohms and voltage
-
I attended a 2 year electronics course at a tech school during '68 and '69. Worked for the Air Force from '70 to '76 doing test equipment calibration and Long Range RADAR. Transferred to FAA and worked Enroute and Terminal RADAR. Retired from FAA in 2012.
I calibrated a few of these Sprague Tel-Ohmike TO-5 Capacitor Analyzers while working in the Air Force PMEL at Robins AFB...
&ab_channel=millstap
-
Looks like our career time line runs almost neck and neck. I took Drafting at a Trade School in 67 and 68, worked as a draftsman at Nabors Trailers from 69 to 81, started working for the US Army as a Draftsman in 81, then Lead Draftsman, Engineering Tech, Estimator and finally Project Manager when I retired in 2011.
Didn't get into any electronics until I got talked into building my first amp in 2000. I really do love electronics. I wish I had discovered that at a lot younger age :icon_biggrin:
Tel-Ohmike with the style buttons, knobs and meters reminds me very much of my Military Tube Tester I use to have. That's a cool capacitor tool that I didn't know existed. I'd say, you need a little bit of training or experience to operate that properly.
I'm glad you decided to apply you electronic knowledge to guitar amps, so you can help us green horns to get our amps to work :help:
-
My big city cousin taught me a few chords and Peter Gun intro when I was 13. That summer he got me a job working in a radio/tv shop, cleaning up, toting a tube caddy on service calls, etc. Been hooked on guitars and electronics ever since. 14 years later he introduced me to Carol. We've been married 45 years now.
Here's the first amp I ever built. I was in my second year of tech school. The upholstery department at tech school did the fancy roll/tuck covering. This was a Sunn Sonora bass amp. I was a wannabe rock and roll star, playing bass for a country band on Friday and Saturday nights. :l2:
(http://sluckeyamps.com/misc/1st_build.jpg)
-
Hay, you should be real thankful for your Big City cousin introducing you to so many great things especially your Wife of 45 years. Did you ever learn Chuck Berry's song "Hay Carol"? :icon_biggrin: Trying to remember my first influential song, I'm thinking "Honky Tonk" or "Pipe Line"? I had a friend Charlie, that played lead to the latest hit instrumentals like Tel-Star, Outer Limits and I played the back up part, all the time learning the lead part on my own.
That's a nice looking strat and amp. You started Big! I'm trying to figure out on the amp, did you have a Sun Sonora and just reworked it a bit? Looks like a Kustom after the upholstery shop rolled/tucked it. Even a Curly Cue cord. I guess truly we all dream of being a rock star at first and then we appreciate what we have left, joy of playing and making good amps
About the time you was doing your gig with the country band I had got rid of my 1482 and Montgomery Ward Guitar, I got a 2-12 6164 Gretsch Variety Amp and Framus Bass. I got this because the top 40 cover band the "ByGones" needed a bass player and they were allvery good. So I worked all the summer to get the rig. After the ByGone gig was Gone>>>>the Gretsch was a pretty good lead guitar amp. The guitar with the Gretsch is a Kalamazoo by Gibson.
-
Did you do your filter caps as well?
Good chance it is the issue.
New filter caps is a must for any old amp.
-
I'm trying to figure out on the amp
My Sunn Sonaro was a scratch build into a brand new Bud chassis. While in tech school I replaced the power transformer in a real Sunn Sonaro (https://sluckeyamps.com/misc/sunn_sonora.jpg), the biggest combo amp I had ever seen. When I saw the simple, clean, true point to point wiring inside, I knew I had to build one. Yeah, the cab was an attempt to make it resemble the old Kustoms.
Here's the schematic...
https://el34world.com/charts/Schematics/files/Sunn/Sunn_Sonaro.pdf
-
Latole
Yes I installed new filter caps but it didn't fix the reverb circuit issues. Also that amp suffered a set back. Not sure what happened but the Vib channel became very weak, vol pot became very scratchy and the plate voltages have dropped.
I kinda got disgusted with the whole thing, buttoned it up and put it up for a while. I will come back to it latter with fresh mind and eyes
-
"scratch build into a brand new Bud chassis"
You lost me on this. What is a Bud chassis?
So yeah, now I understand, your first scratch build. So how did you scratch up the parts in those days? There were hardly any DIY builders in those days, so I know you probably couldn't get everything from one source. Did you take pictures of the Sonaro you worked on to establish your layout and how did that first amp build process go. Last but not least, once you got it fully assembled, how did you bring it up to power for the first time?
I checked out the schematic. Pretty different kind of amp from the normal fender. One thing I couldn't help but noticing is the low "67" plate voltage on the pre Cathodyne PI gain stage, but is also on the PI grid. Kinda different PI arrangement going on there.
Just one more? Did everything work once you got it powered up :icon_biggrin:
-
You lost me on this. What is a Bud chassis?
Didn't even bother to google it did you? :icon_biggrin:
Look... https://www.amazon.com/s?k=bud+chassis
So yeah, now I understand, your first scratch build. So how did you scratch up the parts in those days? There were hardly any DIY builders in those days, so I know you probably couldn't get everything from one source. Did you take pictures of the Sonaro you worked on to establish your layout and how did that first amp build process go. Last but not least, once you got it fully assembled, how did you bring it up to power for the first time?
Parts were easy. I was working part time in the biggest radio/tv/supply house in Andalusia. Everything I needed except the chassis was on the shelves. Chassis came by bus from Grice Electronics in Pensacola. I had no camera back then but I drew up several pages of detailed layout drawings. It's a simple layout. I'll try to find a gut shot on the net. I brought it up in several stages. First power up was for filaments only. Then filaments plus rectifier/filter caps. Finally plug in the tubes. So, three steps, plugged into the wall each time.
I checked out the schematic. Pretty different kind of amp from the normal fender. One thing I couldn't help but noticing is the low "67" plate voltage on the pre Cathodyne PI gain stage, but is also on the PI grid. Kinda different PI arrangement going on there.
Did you also notice the pre cathodyne stage is a pentode? Directly coupled to the cathodyne grid? That cathodyne was a pretty common circuit for hifi amps. A lot of Ampegs used a very similar PI. Did I mention the power amp for these Sunns was a direct copy of the DynaCo Mark III hi-fi power amp (See attachment)? In fact, the very first Sunn amps were an actual Mark III with a separate guitar friendly preamp chassis.
Just one more? Did everything work once you got it powered up :icon_biggrin:
Nope. Failed the filament test. I had correctly put a jumper between pins 4 and 5 of the 12AX7 preamp tube, but I connected the filament string to pins 4 and 5, just like for the 6AN8 PI tube. As soon as I hit the power on switch the entire filament string smoked and melted all the way back to where the PT filament leads attached to the first power tube. No damage to the PT, but I had to redo the entire filament string. Pretty easy fix because the filament circuit was the only thing wired up at that point. Bruised my ego though. I had two classmates watching. By the time I had powered off the whole class was cackling!
I found a gut shot pic of an original. That diagonal cap was not original. Several other components have been changed but you can get an idea how simple this amp was. Lotta emply space under the hood.
-
I found a gut shot pic of an original. ...
Haha!! I'm not the only one that copied Tektronix' layout practice of stringing parts between rows of terminal on either side of the tube socket!
-
I checked out the schematic. Pretty different kind of amp from the normal fender. One thing I couldn't help but noticing is the low "67" plate voltage on the pre Cathodyne PI gain stage, but is also on the PI grid. Kinda different PI arrangement going on there.
Did you also notice the pre cathodyne stage is a pentode? Directly coupled to the cathodyne grid? That cathodyne was a pretty common circuit for hifi amps. A lot of Ampegs used a very similar PI. Did I mention the power amp for these Sunns was a direct copy of the DynaCo Mark III hi-fi power amp (See attachment)? In fact, the very first Sunn amps were an actual Mark III with a separate guitar friendly preamp chassis.
Sluckey, I'm friends with Conrad Sundholm, co-founder of Sunn and heard the story from the horse's mouth - The first Sunn amps were the ones with top mount controls and the smiley face logo. These ones used a Dynakit Mk3 or Mk4 depending on if 60 or 40 watts, and they also used a Dynakit PAM-3 preamp. The actual kits from Dynakit/Dynaco. When the Sunn amps went to a single chassis the preamp circuits were slightly redesigned to be better for guitar and bass, and they still bought the transformers from Dynaco for years after this until they switched to Schumacher. There was also a local Portland, Oregon area transformer used in some of the Sunns - Western Transformer. Conrad bought out his brother Norm in the late 60's and then sold Sunn to Hartzell in 1973 or so and then started Bi-Amp wtith a partner, and sold that years later also. The best thing about the Sunn amps aside from the simplicity was the 2x15 cabinet for the 200S as that was anew thing at the time and really put the sound out there in comparison to other things that were out there in 1964. Somewhere I have a LMS plot from the 2x15 200S cabinet, and one for the 2000S cabinet also that we measured at Conrad's. I'll have to see if I can find it and post it.
Greg
-
Har! I was thinking you was springing some new acronym I haven't heard of yet with "Bud".
Never heard of Bud chassis and they look like they have a good selection.
Must of been nice having access to all those parts in the golden age of tube/P to P electronics. Everything is nicely laid out. I like those 12 position tag strips. Always liked soldering on those! You certainly didn't take any chances powering up in stages. Worst part of the filament burn out is that you had an audience observing.
No I didn't notice the Pre Cathodyne Stage was a Pentode but I did notice the 7199 designation, which I didn't know what it was but have since looked it up that it was a Pentode/Triode like the 6ANB. Also took a look the DynaCo Mark lll. Got to looking for the preamp/tonestack and realized it was just a power amp. So Sun just added their guitar friendly preamp to it and boom! the "Sonaro".
I keep wondering what kind of speakers you had in that cab back then, I'd would guess 2-15.I also would also guess by your last statement that, some of the components have been changed,that you must still have it :dontknow: right?
-
So Sun just added their guitar friendly preamp to it and boom! the "Sonaro".
Not a Sonaro. Their entire line of amps used the same power amp circuit. Slight differences with PT, OT, and power supply, depending on 40W, 60W, and 120W model. Kinda like all the Fender AB763 are the same except PT, OT, and power supply.
There's an interesting story behind the Sunn amp origins. Google "Sunn Shack" if interested. You'll probably want to play Louie Louie. :icon_biggrin:
I keep wondering what kind of speakers you had in that cab back then, I'd would guess 2-15.
2x15 CTS Bass speakers (https://www.ebay.com/itm/274983610791?hash=item40064ce9a7:g:jOYAAOSwLU9hYIul&amdata=enc%3AAQAHAAAAoP3v%2FlUlFnQbSsjMVvUL7sR325yoNxG41QOEM930YhxwOk%2FMKl7IxqGq7Mh%2F3EwppOocTrq9JnK%2F4m3go0R7lCVxbzMNUhEzDDhdaYm91JB5jjZGYoINe07J%2FhUGzX9r06YdoSGf%2BOTh8RFmLFkqd7EtDzI2mMZXtqFLGVvup3mclUZSKx8pzcbBo%2Bl4XH6UEki3Mxc1352XdkVcCIxl6p8%3D%7Ctkp%3ABk9SR6bl_8DRYQ) with big ole square magnets.
I also would also guess by your last statement that, some of the components have been changed,that you must still have it :dontknow: right?
That's not my amp. I just grabbed that chassis pic off the net so you could see how simple the layout was. My clone and the original I copied are long gone.
-
I did some skimming on this thread… so did you ever fix the problem with the reverb? I just got done with a silver face super reverb that had lots of problems. One of them was with the reverb doing a similar thing. On that one it ended up being the .001 coupling cap between the plate of the reverb recovery and the reverb pot.
-
I just got done with a silver face super reverb that had lots of problems. One of them was with the reverb doing a similar thing. On that one it ended up being the .001 coupling cap between the plate of the reverb recovery and the reverb pot.
All the Fender Reverb schematics I've ever seen show a .003µF cap in that position.
-
It’s the 79 ultralinear. The schematic is fuzzy it could be a .001 or a .003 looking at it. However, the cap in the circuit that I pulled out and replaced was .001.
Maybe that explains something about the sound of my amp. I can turn the reverb up really high like 7 or 8 on the knob without getting muddy. The reverb just kind of sits like a shimmer above the note. It is different and I like it…
https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Super-Reverb-Ultralinear-1978-1981-Schematic.pdf
-
I attended a 2 year electronics course at a tech school during '68 and '69. Worked for the Air Force from '70 to '76 doing test equipment calibration and Long Range RADAR. Transferred to FAA and worked Enroute and Terminal RADAR. Retired from FAA in 2012.
I calibrated a few of these Sprague Tel-Ohmike TO-5 Capacitor Analyzers while working in the Air Force PMEL at Robins AFB...
Interesting, I went to tech school for avionics + an A&P license in 1999/2000. First amp I ever rebuilt was in tech school. It was an old Ampeg reverborocket with the octal preamp tubes. My teacher thought it was weird I wanted to work on tube stuff but he helped me anyway. Even though I took all the electronics stuff in tech school, all the jobs I got were always airframe related. I worked for Delta Airlines and Lockheed Martin. I am a data analyst/programmer for Boeing on the 787 now. I have lived all over Georgia an Alabama…
-
Hi Judge74
This project is presently on hold until I feel like messing with it again. Refer to post #41 for an explanation :BangHead:
-
Hay sluckey
Ok, so yeah that was a Sunn Gut shot off the net. I was thinking that was your original---butI'm pretty sure yours was pretty close or better as meticulous as you are on your layouts and lead dress.
I did go to the Sunn Shack and read some of the history. The Kingsmen's Bass player needed a bigger more powerful amp. Because of the rest of the band playing so loud and the crowd hollering and screaming. That's exactly why the Beatles got Vox to build the Super Beatle but I think that SS amp was a dud.
My old high school picking buddy Charlie I previously mentioned has a big Sunn head in his shop.We had talked about getting together and see what we could get it going. Now I'm wondering what model it is?
-
Now I'm wondering what model it is?
I'm curious too. Ask him. It's written on the faceplate. If it's one of the '60s or early '70s it's worth restoring to it's former glory.
This is my Sceptre that I restored back in '06...
(http://sluckeyamps.com/sunn/sunn_01.jpg)
And my Solarus 2x12 cab...
(http://sluckeyamps.com/6v6plexi/P-6V6_09.jpg)
-
That's some cool Sunns sluckey. I visited your site and seen where you installed new 6550's, twin bias pots and test points in your Sceptre. I bet you could get some great loud clean Ventures/Surf tones out of that. Thought it was neat that the Sunn your repaired in School was the one you ended up playing on with the C & W band. You got to test it out real good!!!!
I got my Pro Reverb back out and started doing an all points checkup. Turns out I have several leaky coupling caps in the preamp section. Those I just installed that I thought was good, were apparently shot. So I'm ordering some new from Doug. Hope that does the trick :icon_biggrin:
-
I got kind of a dumb question? Just wondering on this 74 Pro why is the 250pf's in the tone stack, the 500pf to the reverb driver, 120pf bright caps and 10pf on the reverb mixer are all ceramic caps instead of Silver Mica?
The reason for my question is because I bought all Silver Mica for all the ceramic replacements and then got to wondering if there was a reason other than economics for them being in there in the first place.
One More?? Is the "P" following the value on Silver Mica's
same as pf?
-
Ceramics were cheaper and readily available when that amp was manufactured. You may find them to be very reliable too. I can't remember ever having to replace a small value ceramic.
Is the "P" following the value on Silver Mica's same as pf?
yes
-
Thanks sluckey
That clears my mind up about that. I've never known the ceramics to fail either, to the pointI'm hesitant to change them out. On the other hand, never recall a Silver Mica failing either
-
I've heard of "modern" SilverMica failing. Also of SM rated 50V, when all my life 500V was the least you would get.
Also Mica is dug-up by child labor. Not that hundred pF caps are any large part of the abuse, but why buy?
Ceramics to at least 1,000pFd, maybe more, are as perfect as caps get. (Very large ceramics do distort, but do we care?)
-
Well for this amp I'm mostly interested in getting good old classic Fender clean with that deep reverb in the background. Nothing quite like it IMHO. If I want dirt, I got plenty of dirt boxes.
Thanks for this discussion on Ceramic and Silver Mica pf caps. I guess I was wanting permission to feel good about ceramic caps and now I think I can :icon_biggrin: I guess they are like the ugly duckling that is beautiful inside(for the pf range)
-
I believe mica caps are very heat resistant, and are used where there can be little to no variation in capacitance. Ceramics can sway a lot with heat. So in radios, mica caps are used exclusively. In guitar amps, ceramics work well. Although I've heard that ceramics require a minimum of a 1kv rating, otherwise they can be microphonic. That came from BillM's page, so I have no reason not to believe it.
-
OK, I replaced all my leaky coupling caps last night. Looking over all the voltages, everything looks very close within reason of all the voltages except on the PI grid. I would think the PI grids should have 0 DCV but on the one with the .001 cap I got about 65DCV and the one with .1 cap about 69DCV. Don't see anything on the schematic or layout that this should be?
So its coming though the the 1 meg resistors from the cathode voltage of about 100VDC. So based on the PI network of resistors with the 1 Megs behind the coupling caps to the grid, I'm guessing this is normal?
-
I would think the PI grids should have 0 DCV but
You would be wrong. Shirley we've talked about this before?
-
I hate to admit it, but I didn't realize that :BangHead:
We probably have talked about it over the years but apparently I didn't retain it
-
So its coming though the the 1 meg resistors from the cathode voltage of about 100VDC. So based on the PI network of resistors with the 1 Megs behind the coupling caps to the grid, I'm guessing this is normal?
Good guess. This is called bootstrap biasing. In reality, the grid voltage will be only a couple volts less than the cathode voltage. But because of the loading effect of your meter on this high impedance grid, the meter will always show less voltage than the actual voltage. I don't pay much attention to the voltage reading at the grid because I know it's bogus. Instead, I measure the voltage at the junction of the two 1M resistors. That is the same voltage that will be on the grid.
For example look at my Phoenix schematic (http://sluckeyamps.com/phoenix/phoenix.pdf) Same PI as your Pro). Notice there's 78V on the cathode? And 76.4V on the junction of the 1M resistors? That means the bias on this tube is -1.6V. This is my preferred method of checking voltages on a LTP PI tube.
-
Thanks for explaining the Bootstrap Biasing. I think I'm guilty of building amps by the recipe/schematic but not thinking to much of how it all works. If you put it together right with the right parts it's going to sound great just like the original did, but that don't mean you know Jack about whats going on electronically. I'm trying to get better at that!
I was surprised about your Phoenix because I built a Phoenix once but mine was a reverse engineered Dr. Z Carman Ghia. I think Dr. Z was being real secretive about his schematics and there was none to be had, so somebody reverse engineered it, called it "Phoenix" and posted it on the internet. I got a request to build one, so I found and used that.
I noticed in your in Phoenix for your first preamp section you used the Ampeg Gemini ll preamp/tone stack. If you recall, you recommended that preamp for my Bogen CHB-20 conversion and helped me with that. That's a good one, been real happy with that one. I don't think I will forget Bootstrap Biasing anytime soon. Thanks, Platefire
-
Latest Development on the Snake-head Pro. I have gone over and over the circuit and everything seems to be in order to the best of my ability to tell. So I have a new set of JJ 6L6GC's that I dropped in there. Well the bias went hay wire. With the prior set of 6L6GC's I had plenty of play in my bias control to get up to 50 mA or more. Now the setting is topping out at bout 37mA and that's the highest it will go.
I usually try to bias between 60 and 70% dissipation. Attached is a sketch of my bias circuit.I need it to adjust out to about 47mA to get around 70% with the plates at 453DCV.
I think I need to change out the resistor on the bias pot from existing 22K to about 15K? but I'm not totally sure. Is that right? :dontknow:
-
Yep decreasing the range resistor on the pot tail should get you into a warmer bias range. if 15k doesn't do it, 10k should. (All talk, no responsibility)
-
Thanks Tubeswell
This gremlin has been a hard one to chase down. I love a good challenge, but this is ridiculous
-
What's happened to sluckey. He must of took a break?
Well I think I finally may can do a victory lap on this Pro. I changed the bias range resistor from 22K to 10K and boy, that gives me a wide range of adjustment. I biased it up to 65% dissipation and I don't detect any of the former rattling. The thing is solid as rock with absolutely no flab.So that what I was trying obtain. :happy1:
The only thing is last night when i was Jamming on it with that old 22K bias range resistor that wouldn't adjust any higher that 37mA's it had such nice harmonics and it was so touch responsive and I was really getting into that.
So when I biased up to 65% with the new 10K resistor, the response was little stiff and hard. So now that I know it's acting good like a Fender should, I adjusted it back down to 37mA and liking it!! The clean tone is still there, the harmonics are nice and the feel is just all right. So right now it's about at 55% dissipation(I think, plate voltage 443). I'll hang there a while. Platefire
-
What's happened to sluckey. He must of took a break?
Aww, you missed me! That's so sweet. :laugh:
But there was really nothing to say except, YOU GOT THIS! :thumbsup:
-
Well I bought this amp in pieces in a couple of card board boxes. A 1974 Pro Rev, a AA1069. Also who ever had it before me hacked it the circuit with all kinds of mods it looked like they never completed. It's a combo someone cut down to a head. So yeah, I rewired it to AA165 BLackface in 2016. I rebuilt it just enough to get it working back then leaving a lot of old caps and resistors…
1-Turning the reverb up continues to distort the sound. Turn the reverb off and the sound is pretty close to what it should be.
So it had parts from a 74 pro reverb? Including the main board? Did you keep the .002 (2000pF) cap across the reverb transformer secondary? (On the 70s CBS amps, it’s a disc ceramic cap on the main board)
-
Well I think I finally may can do a victory lap on this Pro.
Good the hear!
So it had parts from a 74 pro reverb? Including the main board? Did you keep the .002 (2000pF) cap across the reverb transformer secondary? (On the 70s CBS amps, it’s a disc ceramic cap on the main board)
I was just looking at that cap & the other "new" cap between the plate & cathode on the reverb driver tube. Were these both added as part of the CBS noise-reduction effort?
-
Hay sluckey, welcome back. It's just when your so active answering everybody's questions andthen disappear, makes you wonder :dontknow: You need to put it a "Request for Leave Slip a34jub-00##" for approval before you go!!!
tubeswell----I don't recall ever seeing that cap across the reverb transformer secondary. I basically removed all the non-fender mod stuff someone had added to the circuit. Then I rebuilt what was there to AA165 schematic. I see it is on the AA1069 schematic. Anyway it's not there now
tdvt------I looked at the AA165, AA1069 & AB668 Pro Schematics and don't see that cap between the plate and cathode on the reverb driver tube. Can't say for sure I never removed it, that was 2014. This circuit was seriously hacked before I got it, so I built it back AA165 so I would know what I got. So it may have been there previously but I don't see it now. Yes I know CBS did a several circuit additions to combat previous noise issues in the 70's but like I said, it's all AA165 now with the exception of a Bassman OT, sluckeys Tremonator, bias bal pot to bias adjustment pot mod and am using a 5U4 rectifier instead of a GZ34.
So much for the cool bias noodling. I tried my hotter humbucker guitars on 37mA bias setting and they was distorting a relatively low volumes. So I went ahead a jacked it up to 43mA to get a balance between tele to LP. Platefire
-
> You need to put it a "Request for Leave Slip a34jub-00##" for approval before you go!!!
So dock his pay.
-
Yes 50% of his next paycheck and plus, shame on him for at least 30 minuets or even longer!
-
Nothing from nothing leaves nothing.
I took permanent leave on 12/31/2012. :l2:
-
Ain't it Nice :m11
-
Is it possible to Ohm test an OT without pulling the chassis? I did try by going through the Rec socket pin 8 to center tap(standby off) and through the 6L6 sockets pins 3(plates).
I got 38 Ohms between center tap and on one socket and 53 Ohms on the other. Got 90 Ohms between plates. .5 Ohms between Primary leads and .4 Ohms between secondaries.
I figure that this is not too good being also connected to the dog house caps through the choke and also to the Reservoir caps. I just hate to pull that chassis on this head converted from a combo, because it's so hard to get it out and back in.
Anyway I'm still getting low power and grit along with the clean sound. It sounds pretty good up to 3 and the louder you get past that the grittier rattling gets worst especially on the low note cords.
I'm now suspecting the OT of being bad. It came with the amp. Its a New Sensor NSCO18343 Rev B 238-9544 Bassman type OT. I got it with the amp parts and it looked brand new plus the leads looked like they had never been hooked up. So if I have to pull the chassis again to test it properly, I will. Platefire
-
The primary plate leads looked OK... until you said this...
.5 Ohms between Primary leads
Please clarify. Exactly where was each meter lead?
-
Ok, I went back and re-took those measurements just to be sure.
The measurements between the primaries were correct.
The measurements between secondaries was just between the green 8 Ohm speaker tap andthe black ground-.5 Ohms
Also measured between primary and secondaries. CT to 8 Ohm green speaker tap started at1.3M descending toward "0"
CT to black speaker ground started at 20M descending toward "0"
-
Well, kind of embarrassing to think you got your problem fixed and it's not. I think I can safely say that the OT is good.
One thing I'm pretty sure of is the rattling gritty sound is related to the reverb because I can remove the cables either or just turn the reverb off with the knob or foot switch and the rattling is gone.
One potential problem is the fact that there is only about 1/8 to 1/4" separation between the bottom of the OT and reverb tank. I did try to stick some aluminum foil in between the OT and R tank but no change. Of course it's so close that the foil was touching the tank and OT, so with that I don't know if that shielded anything.
I know grounding of the reverb cables to the amp chassis and reverb chassis can be a problem.I checked that and the reverb in cable is grounded to amp chassis but is not grounded to pan chassis. The reverb out cable is grounded to both amp chassis and to pan chassis. To my understanding, that's the way is should be?!?
As far as the amp chassis reverb circuit, I installed a rca jumper from in to out reverb jacks on amp chassis, bypassing the reverb tank. The sound with the reverb turned on adds gain and a treble boost but none of the rattling. The more the reverb is turned up creates distortion but in even harmonics, not gritty rattling. So considering the very small reverb signal that requires a lot of boost, I would think this is normal.
So something is this reverb loop is amiss but so far I can't lay a finger on it. If you see something I stated wrong or I missed, please let me know. Thanks, Platefire
-
The combo cab has been cut down to a head unit, right? Pull the reverb tank and use some longer cables so you can move the tank around on the bench top. Any joy?
-
yelp, already done that with plenty of separation between tank and amp. Tried it with three different reverbs with the chassis out---the reverb in the Pro head cab, the reverb in my Accomplice and in my Pacer/DR conversion---all no change.
It's in the reverb loop circuit. Turn the reverb off it's gone. It's a odd harmonics distorted rattle and the more reverb you dial in, the worst-er it gets. The reverb sounds good, it just brings with it this odd distorted rattle especially accentuated on the bass notes.
Got me :think1:
-
But you bypassed the tank and had no rattle. That seems to indicate the circuit is OK.
-
Yes bypassing it with a rca patch cable it dialed in even distortion. I played around with it at different settings. Produces some very good OD except it is a little too bright for me.
So that seems to indicate that the problem is the tank! but doing the same thing with other tanks seems to eliminate that idea?
Last thought I had is since the reverb sounds normal and the noise gets worst as the reverb is dialed up, makes me wonder if the problem is after the reverb control pot on the return. Could a bad cathode bypass cap or resistor do that on V4 shared 820 cathode resistor/25uf cap? I've tried several different good tubes in that location with no change.
-
A lot of people use separate resistor/cap on V4 cathodes. Need two 1500Ω and two 25µF.
-
One thing I'm realizing about this amp is it only has about 50 to 75 % of the volume it should have at 10. That's what made me suspect the OT. Double checked power tube screen and plate voltages and they are good. I've gone over PI wiring and voltages and haven't found any problems. Checked for incorrect component values, but haven't found any. Done continuity checks all across the circuit.
This amp seems to be dodging every punch I make at it. I don't find anything really off but the overall power is not what it should be and the noise in the reverb persist. :BangHead:
This is one of those amps that test your endurance to the max :angry:
-
I think I've found the low volume problem but it wasn't what I was thinking. I was out tending to some appointments and put my hearing aids in. When I got back home before I took my hearing aids out I picked up my strat and plugged it into the pro. Wow! with my hearing aids the amp sounds pretty much as loud as it should be :think1: I knew I had some hearing loss, but didn't think it to be that bad. I haven't been using the hearing aids only occasionally but I I've got to! I will just have to get use to playing with hearing aids. So I'm going to declare I think this is the low volume problem pending further testing, with the hearing aid of course!
Reckon if I cranked up that hearing aid amp, I could get a little saturation??
-
....I knew I had some hearing loss, but didn't think it to be that bad.....
It gets more every year.
I should call for an appointment to tune-up or upgrade my aid.
The usual advice in the aid-using community is to wear the aids "all the time", except sleeping or mowing. (I assume you have good muffs for when you mow, hammer, etc.) Hearing is tricky and your brain needs that much practice.
> The amp is now dead silent as far as operating noise
That's another clue. I noted that one side of my stereo monitor hissed. No, actually the other side did not hiss. But did if I used my other ear. I lost my "hiss frequencies", one ear before the other. (The other was not that far behind). Now my "dead silent" is moderately loud to a "normal" ear.
And like my grandfather, I can hear thunder on the other side of the county better than anybody. (And UPS trucks before the dog, but I think she is losing it too.)
-
couldn't get my decimals to land in the right place.
1uF is a millionth of a Farad 0.000001F
1nF is a thousand-millionth 0.000000001F
1pF is a million-millionth 0.000000000001F
-
PRR---Second thing I noticed after the extra volume I was missing is I had to turn down the treble---way too bright. Also another sign, I use to never use the bright switch, but lately I've been using it.
One good thing though, even with my hearing aid in, the amp is still real quiet. So it's either one of two things, my hearing is too far gone for even a hearing aid to help or either the amp is actually quiet---ehh
Tubeswell----Thanks for the actual breakdown of decimal places. Something I can refer back to. I also refer to a "Capacitor Conversion Chart" that has side by side comparisons of the same value for uF, pF, nF and K
-
> my hearing is too far gone for even a hearing aid to help
They can help even profound hearing loss. Find a good audiologist.
(I don't think much of the current trend to self-prescribed aids. Even as a lifelong soundman, the adjustments for hearing are not easy/simple.)
-
Yes I think my insurance covers a Preferred Provider audiologist and prescribed hearing aid, I need to check into that. Right now the wife and I in the process of Cataract Surgery in both our eyes.
On the amp, if I can figure out the reverb circuit Rattling odd distortion, then that amp will be up to snuff!
-
This is a you tube video but there is no video, only audio. This is the amp noise my Pro Reverb is making with the volume set on 4 and Reverb set on 3. It's a rattley fuzz like distortion as I strike it on the bass strings in open E. It should be clean tone. I've done a lot of research lately on the net to find a similar noise problem on a fender reverb and have not found another.
It only occurs when the reverb is on. With the reverb turned off with switch or by knob, the amp is clean, as it should be.
If you got any ideas, let me know. I'll be diving in soon to find it. Platefire
eature=share
-
Dredging up this old thread as I was wondering if you ever found the culprit?
In the end, I decided to keep my UL Pro Reverb project (https://el34world.com/Forum/index.php?topic=30026.msg330846#msg330846) in a stock configuration channel-wise & while checking things out before it went back in the cabinet, I realized I have a very similar rattle/distortion as you posted in your YT video. Low E/open E chord break up more than I would expect, upper register sounds normal.
I am not sure my issue is reverb circuit-related, but need to go back though it now that I have re-read your thread.
-
Yeah, I changed out everything with new that was questionable and did everything I was suggested to do or could think of and the rattling persisted. I finally just had to give it a rest because it became to much of an obsession to me. So I put it up and moved onto other things.
About a month later I took it back out and tried it and low and behold, it was working fine and still does to this day :dontknow:
-
About a month later I took it back out and tried it and low and behold, it was working fine and still does to this day :dontknow:
I don't usually have that kind of luck.
Sounds like the shoemaker's elves got to it before you did.
-
About a month later I took it back out and tried it and low and behold, it was working fine and still does to this day :dontknow:
I don't usually have that kind of luck.
Sounds like the shoemaker's elves got to it before you did.
I once took a fine Brownface Concert to a friend's gig to let him borrow it. Unloaded it, plugged in - very low volume. I was running the soundboard, so only had a few minutes - could not find the problem. Took it home and the next day removed the chassis to troubleshoot. It worked fine :dontknow: While I had it open I cleaned up some sketchy solders. I never did figure out what the issue was, but hope that cleaning up those solders fixed the unknown.
BTW - don't ever volunteer to run the sound. Every band member wants it different.
-
I've always thought I would enjoy running sound but I was always occupied in lead guitar or occasionally bass slot. Knowing how bands work(especially the lead singer) :argue: , I could see that it could be a very uncomfortable position to work.
-
I'm wondering if you are not simply swamping out the reverb pan. How does the reverb sound on around 3 or 4 with your hearing aids in?
Some observations that I have about the reverb circuit... May not have anything to do with your problem...
Cathode ground on reverb return is prone to ground loops. A loud enough hum from a ground loop "could?" be related.
Sometimes a 12BH7 sounds better as a reverb driver than a 12AT7.
Sometimes the springs on a really old tank can get a little loose and flabby and make it easier to swamp out.
Dave
-
BTW - don't ever volunteer to run the sound. Every band member wants it different.
Somehow, I was always the default sound guy (from the stage) Thankfully, most of the guys over the years were reasonable....but not all
Just ran some quick voltage checks/guitar test on my Pro. My rattle/distortion is NOT reverb circuit-related, but in the process I found some significant board leakage, in spite of extensive cleaning & de-waxing. Thought I had that addressed, but apparently not.
Seriously considering just building a new board for it & moving everything over.
-
Fender boards - As I understand it, the original problem was moisture in the boards. And then Fender "corrected" it by waxing the boards. So now we are dewaxing the boards. What is to keep the moisture problem at bay, I wonder? Is there another product that might seal the board after dewaxing? It would need to have a high melting temp and be non-conductive. I see that folks melt and clean the wax off, and then finish up with isopropyl. I think it is down to bare cardboard at that point.
-
This is what my Pro board looked like when I got it. As you can see, a real mess in more ways than one. The guy that sold it to me believed it would never work again without a new board. Not only was it filthy but wavy as the sea. As I remember, I cleaned this one with Isopropyl. I never have detected any conductance through the board. It's really working right now like I always wanted it to.
Dave--I think you are referring to me? Yes, if I have to do any serious critical listening with my hearing aids in because of not only the volume loss but treble/highs loss. Previously before I changed out a lot of parts, when you turned up the reverb up it added serious amounts of gain to the signal plus more humm. Now I can detect an ever so slight amount of gain, not enough to bother with. The reverb just gets deeper when you turn it up now, with no hum.
-
Those are some scary pics!
I have 0 to a few mV DC in some areas, but I was seeing 3V± in the bad sections & was able to induce noise into the circuit by scratching the board with the meter probe.
Visually, the bad areas look as clean as the good sections & had similar heat gun/iso bath treatments.
If I have to depopulate the board for real cleaning, I am thinking I'd rather just move stuff onto a new one & would probably use some garolite/bakelite sheet that I have in stock from making tele pickguards.
That stuff is a similar thickness to the original eyelet boards but seems to be much more stable.
-
I think I used Q-Tips, tooth brush and Isopropyl Alcohol to work around under everything on the board. It was pretty painstaking but I was just determined to make it work.
-
I took custody of a second '79 UL Pro Reverb yesterday & while not nearly a waxy as the first one, it too, has significant board leakage.
I am seeing around +2V on the board near the preamp tube B+/100K eyelets.
On the little rectifier board that the bridge rectifier lives on, I am seeing +5V to +6V, well away from any eyelets.
This one is completely untouched inside & in spite of the old original e-caps & the board leakage, is essentially fully functional (other than weak trem) & surprisingly quiet.
-
Me, being that it's operating without any problems presently, I would clean those areas with Alcohol and then dry it out with a hair dryer and call it good.I would check resistors, coupling caps and definitely change filter caps being 30+ years. On the Trem---put in one of sluckey's Tremenators--they nice and clean, no ticking and no more bugs to change out
-
Me, being that it's operating without any problems presently, I would clean those areas with Alcohol and then dry it out with a hair dryer and call it good.I would check resistors, coupling caps and definitely change filter caps being 30+ years. On the Trem---put in one of sluckey's Tremenators--they nice and clean, no ticking and no more bugs to change out
I will admit I am torn; on one hand it is working, on the other hand, for how long?
I am guessing that it was left for dead a while ago. I received it in pieces, directly from the storage locker & there was no sound when I first put it on the LL. But just a couple broken coupling cap leads. Replaced those parts & off she went.
I actually haven't finished the first one to my satisfaction (occasional static I am attributing to the noisy board) so probably best NOT to go to deep on this one yet.
Don't know if you have ever checked out Brad's Guitar Garage on YT. He's been up to his eyeballs on a few different silverface rehabs with some rather intensive board cleaning, seems to be a thing with this era amps particularly.