Ampeg B-12-XY....

[Jack_Hester]

I'm at it again.  Maybe I won't be so lengthy with this thread, though I can't promise.  The poor old Falcon will just have to wait.  Glad it belongs to me.

I figured as I had my first older Ampeg behind me, I would stay on a roll.  I have a similar model, in B-12-XY configuration.  I've got it close to the basic working condition as the last.  It was purchased as a 'working' amp, but the hum was so very loud.  Not in much of a working condition.  Glad it was reasonably priced.  Here is the schematic that I'm working from:

http://www.el34world.com/charts/Schematics/files/ampeg/Ampeg_B12XY.pdf

Anyway, I decided to clean up the wiring in the cabinet first.  I removed the speaker and horn.  The speaker had four repaired tears.  I found a fifth tear.  The four had been glued, but that was all.  I covered them each with a patch of glue saturated paper towel, as well as the tear that I found.  Dried them with my heat gun.  The horn was non-working.  Someone had been inside of it, as both speaker coil wires were broken off.  One, flush with the cone.  I'll have to see if I can find a replacement cone.  Got the cabinet insides cleaned up and new speaker cable strapped in and soldered to the connector.  I left a piece attached for the horn, whenever I have it repaired or replaced.

I replaced the speaker cable connector with a new one, as the old was some damaged.  I also cut and stripped back the cable end, going into the chassis, remembering how badly the last one was damaged.  It already had a grounded cord, but I did the same with it.  Stripped it back and reconnected.  

This amp has had 'hands-on', in it's past, and was very trashed in it's appearance.  I won't go into all the detail on what I found, but I made note of each non-standard component and where it was attached.  Then, I removed them all, and put them aside just in case they could be reused.  I started with the power supply by removing the canned decoupling capacitors.  The schematic shows C49a,b,c,d to all be 40uf.  And, C48 to be 30uf.  I had a can that had two 40's, and two 20's, an extra purchased for the last amp repaired.  I installed this one, and paralleled a .22uf with each 20uf.  

Then, I began my testing with all tubes removed.  A note here about the tubes.  I tested all of them on my B&K 707, and the 7199 was bad.  I had only one on hand, and it tested good.  All the rest were in good shape.  I powered the amp and measured the mains and filament voltage.  I did not record them, as they all showed higher than normal, with no load.  

Next, I put the rectifier tube in, and powered the amp on my lamp limiter.  Standby on, 25W, 40, 60, and 100.  Then with full line voltage/current, I took the same readings for it, plus the DC out.  Those were satisfactory.  I installed the power tubes, and when I put power to them, I got a very load hum in the speaker, with no B+ (standby switch was open).  Shut the power off quickly and removed those tubes.  I did not check the Bias voltage before, so I turned the power on and checked it.  I had a negative DC downstream of the diode.  So, I checked everything around it, by the schematic.  C36 was missing.  It's supposed to be a 100uf.  I looked at my notes, and I removed no cap from this location.  I found a new 100uf and I pulled a 47uf to try, also.  Installed the 47uf first.  Put the power tubes in and powered it up.  Only a slight hum, more like a buzz, was present.  Very low.  I put the 100uf in, and made the same test.  Same buzz, so I left it in.

I went back and put the 100W bulb in and one at a time, I installed the remaining tubes turning the power off between each.  And, listening for a change in sound as I closed the standby switch.  V8 generated the first hum, though it was not very loud.  The rest made no difference.  I grounded V8-pin9 and the amp got quiet.  I moved over to V5-pin4 and grounded it.  Amp went silent.  Moved over to V6-pin4 and grounded it.  No change in hum.  So, it looks like it's in between these two tubes.  I'll not chase this one yet, as I want to do some more checks on the rest of the amp.

A note here.  Vibrato does not work.  And, the Echo is ever so weak.  Turned up full, you just can hear a difference.  But, you've got to listen for it.  I won't chase those just yet.

Jack

[Jack_Hester]

I got cut off with too many characters on the last post.  Here's the rest.

I made whole-amp voltage readings and put them in a table.  Figured it would be easier to read than the manner that I posted them on the last amp.  They are attached below, in a graphics file and a pdf.  

Please note the highlighted voltage in the table.  It is a little better than twice the value stated on the schematic.  Right now, I'm thinking C33 needs replacing, but I'll await comments.

Anyway, that's where I am now.  I took the opportunity to come to the house and warm up.  The shop was 39°F when I left.  The sun is out, so it should be warmer in there, now.  I'll post my findings as I go.  Have a look at my data, and please comment.  Thanks for all the help.

Jack

[Jack_Hester]

I am finding some wiring discrepancies between this amp and the schematic that I downloaded.  This amp does not have one glued to the chassis platform, like the last one did.  The Echo tank is in that spot.  If any of you have an original that you can scan, I would greatly appreciate it.  

I sent an email to Loud Technologies, but don't expect an answer for awhile.  Until I can find an accurate one, I'm just going to have to blow this schematic up and divide it into sections.  Or, find somewhere to print it on an 11"x17" sheet, so that I can mark it up as to how this one is built.  Then, I can CAD a correct one.  This alone is going to slow this troubleshooting down, greatly.  But, I'm working on it.  Have a good one.

Jack

[Jack_Hester]

Ok, did a little search.  Seems that a couple other people have run into the same situation.  One of them posted a hand-drawn schematic of the Echo circuit.  I haven't confirmed it with mine, but more than likely it is the same.  I've attached it below.  I'll confirm tomorrow afternoon, after Church.  Have a good one.

Jack

[sluckey]

And, the Echo is ever so weak.

You did not mention the separate small speaker cab used for the echo. Do you have it? You must have a separate speaker to hear echo (reverb) from this amp.

I don't trust that hand drawn schematic. Output stage looks whacky.

[PRR]

> Output stage looks whacky

I think the OT is drawn in two pieces. If you slide the secondary up-over next to the primary it looks conventional.

[Jack_Hester]

You did not mention the separate small speaker cab used for the echo. Do you have it? You must have a separate speaker to hear echo (reverb) from this amp.

I don't trust that hand drawn schematic. Output stage looks whacky.

Yes, the speaker cabinet is there.  Let me clarify a bit, about the Echo.  The signal from the spring tank is amplified very well.  But, I'll reserve judgement on that, until I have it all assembled, and the amp is riding on the rubber mounts.  As it is, laying on the table top, I can thump the table, and get a very good echo from the little speaker box.  Rather clear and loud, though I don't know how it's supposed to sound, as the larger speaker is capable of so much more than the two little ones in the box.  Anyway, I'm thinking that the signal driving the tank is not getting through, though I haven't gone that far in my troubleshooting.  I had another Hammond tank connected to it, just to verify.  Not knowing the impedances of either, I hooked it up briefly as a comparison.  Same results.  Weak.

I don't trust the hand drawn schematic either.  When I have my own markup, I can verify it.

This would be a rather busy schematic to CAD.  At least for now.  What I'm planning on doing first is to take the original (blown up in size) and mark it up as to how my amp is wired.  While I'm at it, I'll see if I can't put in some better component labels, values, and any other items that might need better identification.  When I'm to that point, and I'll be troubleshooting at the same time that's happening, I'll decide if CADing is necessary.  

Though the work on the last Ampeg had me scratching my head quite a bit, it was way more basic than this one.  Fortunately, after the cleanup of the chassis and speaker cabinet, and replacing the missing component(s), this one is working at almost the level of the last.  It still has some cleanup of the slight buzz to be done.  But, getting the schematic in good order is a priority right now.  And, I may find some of the issues as I do this.  I'm thinking that the resolution of the Echo will come along first, before the Vibrato.  Already, the caps in the Vibrato don't match the schematic.  The ones with the value of .022uf in the schematic, are actually .01uf in my amp.  Which way do I go with those?  I know that some of my background hum/buzz is coming from that direction.  But, it's not annoying, yet.  At least, until I have all things working.  Then, the chase is on, for that.

I think the OT is drawn in two pieces. If you slide the secondary up-over next to the primary it looks conventional.

I'll confirm this, hopefully within the next day or so.  And post my findings on a copy of the original.

Work hours are rather long for the next week or more, so work on the amp will be minimal at best.  But, I'll keep nibbling at it, until I can spend more time.  Thank you for your comments and please keep me on track if I head off in the wrong direction.  I'll try to post my moves accurately, and not depend on a poor memory.  More to come.  Have a good one.

Jack

[sluckey]

If you slide the secondary up-over next to the primary it looks conventional.

Yes, I considered that. But the 68µF between the secondary and the RCA speaker jack still looks whacky.

[Jack_Hester]

the 68µF between the secondary and the RCA speaker jack still looks whacky.

16:05 hrs. -  I got out here at 15:00 hrs..  I don't know when I'll finish a markup of the schematic, but what is labeled as V8b,c is actually V7b on the left and V8b on the right.  And, I have a 50uf-50v cap between the secondary and the RCA connector.  It's not on my schematic, but it is original to the amp.  

And at this point, I have verified my amp Echo circuit. Substitute V7b for the left triode, and V8b for the right triode, and it's wired very much like the drawing.  R67 is shown as a 5.6M resistor in series with C39, a .001uf cap, connected to a tie point on J6/8 ohm OT secondary.  Mine has two(2) 5.6M resistors in series, those being in series with C39.  Maybe that's a reason for the weak Echo.  

V9 is just as it's drawn.  I just made a quick comparison with the hand sketch that I posted, from the other fellow.  I believe that he has it very close to mine.  Also, my footswitch is like his, in series with R71 to V7-pin6.  Not like the schematic.  

Lastly, there are about a half a dozen component value differences, from the schematic.  I'll show those in my markup.

Anyway, I'm calling it quits for this evening.  I'm glad to have the Echo circuit documented.  Of course, the remaining triodes of the V7 and V8 have to be sorted out the same way.  I'll see if I can't get what I've found marked up on a drawing, tomorrow.  

More to come.  Have  good one.

Jack

[PRR]

> the 68µF between the secondary and the RCA speaker jack still looks whacky.

Ah. I understood it as a bass-cut. 68u+8r= 300Hz, very reasonable to take the heavy boom/bang/mud out of a spring tank.

There's also 170Hz cut going into Echo Dim pot, and 340Hz cut at 6AQ5 grid.

That cap is drawn as polar electro. And there's pretty good power available. So it will crap-out "young". I've done similar caps as crossovers and they work for years. What was Ampeg's original warranty?

Yup, by now it sure is time to find 68u NON-polar in 25V or 50V rating. PartsExpress tends to have some low-cost options (this isn't a place for silver-foil and mink-oil caps). Or two 150u 50V polar electros + to + in series.

Or strap it. Signal will pass. I suspect it is about the specific speaker they used: great mid-high output but didn't handle bass gracefully. Since reverb for effect is mostly midrange, bass-chop is appropriate, but strapping will tell you signal gets through.

[xm52]

There are a few amp variations in the B-12X series including the B12XY, B12X-B18X and the B12XT. I think that it would help to look at the schematics and compare them. Here is a copy of the B12XT manual and schematic (http://www.vintage-blue.us/blog/schematics/b12xt_manual.pdf).

Concerning the phase inverter pin-9 voltage. Yes it looks off. The pin-3 voltage is usually a lower than pin-9 but not by the amount that your reading revealed. I would check out the voltage divider resistors that connect to pin=9, R56, R57, and R58, are the correct values and are up to spec. The B22X has pin-9 of the 7199 at 115V, so higher voltages than those seen in the XT are not unheard of.

Here is a copy of the B12X schematic. I don't have a better copy of the XT one.

[Jack_Hester]

Or strap it. Signal will pass. I suspect it is about the specific speaker they used: great mid-high output but didn't handle bass gracefully. Since reverb for effect is mostly midrange, bass-chop is appropriate, but strapping will tell you signal gets through.

Please explain strapping.  Thanks. 

Jack

[sluckey]

Please explain strapping.

Put a jumper wire across the cap.

[Jack_Hester]

I would check out the voltage divider resistors that connect to pin=9, R56, R57, and R58, are the correct values and are up to spec.

R56 is a 100K.  R57 and R58 are the values shown on the B12XY schematic.

Jack

[sluckey]

I would not worry about the voltage on pin 9. That PI circuit uses bootstrap biasing which causes the grid impedance to be verrrry high. Meters with a 10M input impedance will load the grid and cause the voltage reading to be much lower than it actually is.

[Jack_Hester]

10:55 hrs. - Ok.  I believe that I have tubes V7 (6D10) and V8 (6D10) verified, as to where they belong on the schematic.  

On Channel 1 (J1, J2), V7a is correct as drawn.  V8c is after the tone stack, instead of V7b.  

In the Echo circuit, V7b is the first triode, instead of V8b.  V8b is the second triode, instead of V8c.

In the Vibrato circuit, V8a and V7c are correct as drawn.  

Both Vibrato and Echo depend on their cathode resistors being grounded through the footswitch, to work.  Both switches are so intermittent that I will replace them.  For now, I have alligator hard jumpers in place.  Vibrato doesn't even attempt to work.  

In all fairness, the Echo may very well be as loud as the two little speakers will let it.  They are 4" speakers, and with the Dimension pot at full, I can pluck a string and dampen it, and I hear the sound/echo in these speakers.  And, it is not quiet, if I test it that way.  This would make a nice little amplifier, by itself.  If it were mic'ed separate from the main speaker cab, it might sound good.  The 12" speaker just drowns it out.  I'm beginning to think that if I had a 12" connected to the RCA jack, I would hear much better 'Echo'.  

I'll put this circuit aside (in the troubleshooting) and move on the the Vibrato and the buzz.  I had almost forgotten about the buzz, as it is so subtle.  But, I have the B-12-N to compare, and it is quiet, with no such buzz.  I'll go back and revisit it by grounding grids, now that I have a usable schematic (markup, that is).  More to come.  Have a good one.

Jack

[Jack_Hester]

I'm in a verifying mode.  I'm going to do so with all the components in the Vibrato.  No detail for every one, just yet.  But, the most obvious differences are C13,14,15, and 16.  They are all .1uf in my amp.  All other Vibrato details will be posted on the corrected drawing, for the whole amp.  Those just stood out. 

Jack

[Jack_Hester]

16:55 hrs. - The entire amp has been verified and markups made on my drawing.  I printed it in four large (8.5x11 each) sections, so that I could make notes. 

Just took a bias voltage reading: -51.5vDC. 
Measured the bias current on each tube: V1 - 28.2mA, V2 - 26.3mA. 

So now, I need to figure out how to make a high resolution drawing with the notes.  Windows Paint just don't get it.  I'm unable to save as a high-res file.  Right now, all I have the schematic saved as is a pdf file.  When I copy and paste the schematic into Paint, it is lower resolution than the pdf.  I tried another graphics editor with the same results.  I think that I need to start with a high resolution graphics file and go from there.  I'll post my progress.  Have a good one.

Jack

[Jack_Hester]

The heck with learning a new graphics editor.  I can do it in CAD, so I started making a new schematic from the original.  I forgot to bring my notes to the house.  But, using what I posted here, I can at least get the tube nomenclature correct.  That will be rev A.  I will update the drawing with my component values and cal that rev B. 

So, here's as far as I got this evening.  Long hours start tomorrow (Tues), and for the next 8 days.  I can try to add a little to it over that time.  More to come.  Have a good one.

Jack

[Willabe]

The heck with learning a new graphics editor.  I can do it in CAD

That looks real good Jack. Way better than Express SCH, which is what I use.
              

                    Brad    

[Jack_Hester]

Brad -

I started to use Express SCH.  But, I already have my symbols library in good shape for tubes, in AutoCAD.  Not very well organized, or clearly labeled.  For someone else to use.  But, I can find just about everything I need.  So, I'll just wade through the schematic and build it a section at a time.  A bit easier time doing this, than hand-tracing it to verify by the old one, like I just completed.  That took a while. 

I really need to organize my symbols library better, and rename the symbols to be clearer.  Stuff like that is my rainy day/cold and nasty weather kind of stuff to do. 

Anyway, it's coming along.  I might even make a layout of the eyelet board.  It's fairly cut and dried.  I know that it's 2" wide.  And, the eyelets are on a 3/16" (or was it 5/16") spacing.  I don't have symbols made for actual components.  But, a layout with electronic symbols would be a start. 

Jack

[Jack_Hester]

Just a little on rev-B, which reflects my actual amp configuration.  

I just noticed that even though this is the makings of my amp, I still have the component values from the actual schematic, which will be rev-A.  When I'm finished with both, they'll be correct. 

Jack

[Jack_Hester]

I'm still chiseling away at the rev B version of my schematic, 30-45 minutes or so, when I can.  I've also begun the process of troubleshooting the Vibrato circuit (in my head), and wondering where to start with cap replacements.  This portion covers a lot of ground, compared to the rest of the sections.  Should I just go ahead, bite the bullet, and replace all caps from V5, V6, V8a, through V7c?  

That is a whole lot of caps at one time.  Or, should I take one tube section at a time, and see what happens?  Or, is there a definite starting point on an oscillator to look for trouble?  I know the Channel works without it.  And from the drawing, the signal wiggle from the oscillator to V3 originates at R29.  

I've already changed the cathode cap C23, on V7c.  I did that up front, as part of the cleanup.  It had a big ol' clunker stuck in there, and I put a 25uf-50v back in it's place.  I don't know if it really needed that high of a voltage rating.  But, I had one, it was small, and it fit nicely on the eyelet board.  

This is one of the sections of my amp where the component values (mostly caps) are different.  The .05's have .047's in place.  I don't consider that value difference to be an issue.  But, I'll let someone else speak up and clue me in.  Also, most (if not all) of the .022's are .01's on my amp, in this section.  I would consider this to be a point of concern, if they had been all replaced with these values.  But, they have all appearances of being original to the amp.  

The first time that I tried the Vibrato was the last test, after going through the steps with the lamp limiter, testing the rest of the amp, and doing some additional cleanup.  When I tested it, I had a guitar laying over on a bench, and connected to Channel 1, volume, treble, bass at 12 o'clock.  I did not use the footswitch.  I strummed the guitar to have a sound coming out of the amp, and jumpered the footswitch teminals.  Vibrato Speed and Intensity were at 12 o'clock.  There was an oscillation that began, died down to none.  And, it hasn't worked since.  Having no real history of the amp, I'm assuming that it's been sitting for quite some time.  

Anyway, that's where I am.  Can't spend any hands-on time with the amp.  Just drawings and looking at them as I go.  Please study and comment as to a good direction to start, when I can get back to troubleshooting in the shop.  Thanks for all help.

Jack

[sluckey]

Should I just go ahead, bite the bullet, and replace all caps from V5, V6, V8a, through V7c?

No. Divide and conquer. Make the oscillator V7c work and the rest of the trem circuit will probably work.

Remove the lamp limiter if still connected and plug the amp straight into the wall. V7c needs full B+ to operate. Check voltages on plate, grid, and cathode of V7c. If oscillating properly the plate voltage will be fluctuating at the trem frequency and will just appear erratic on most dmms. A scope or analog meter would be very nice to monitor the plate. The trem signal on the plate should be a BIG amplitude low frequency AC sine wave. You can view this signal with a scope. Or, your dmm might be able to measure it. My Fluke 87 can measure the RMS voltage as well as read the frequency of most tube trem signals.

If your V7c is not oscillating, swap V7 and V8 first, or subsitute a good tube for V7 if you have a spare. If still no go, change C20, C21, and C22 (.047µF is fine). Next check resistors in V7c circuit and measure resistance to ground for the grid and cathode.

Hopefully the trem will be working at this point. Let us know the results of these few checks.

[Jack_Hester]

No. Divide and conquer. Make the oscillator V7c work and the rest of the trem circuit will probably work.

Remove the lamp limiter if still connected and plug the amp straight into the wall. V7c needs full B+ to operate. Check voltages on plate, grid, and cathode of V7c. If oscillating properly the plate voltage will be fluctuating at the trem frequency and will just appear erratic on most dmms. A scope or analog meter would be very nice to monitor the plate. The trem signal on the plate should be a BIG amplitude low frequency AC sine wave. You can view this signal with a scope. Or, your dmm might be able to measure it. My Fluke 87 can measure the RMS voltage as well as read the frequency of most tube trem signals.

If your V7c is not oscillating, swap V7 and V8 first, or subsitute a good tube for V7 if you have a spare. If still no go, change C20, C21, and C22 (.047µF is fine). Next check resistors in V7c circuit and measure resistance to ground for the grid and cathode.

Hopefully the trem will be working at this point. Let us know the results of these few checks.

Divide and conquer is what I like.  Thank you very much for the starting point. 

I'm past the point of lamp limiter.  It's been on full line voltage/current for the last several times that I've had it on.  I'll use my VTVM for this.  I look for opportunities to use it, as they don't come often.  I'll compare with the Fluke 8062A, but I like the idea of watching a big needle swing.  No doubt about oscillation there. 

I'm fairly sure that I've got some 6D10's, though I'd have to look for them.  Both these tested very high, but that don't always tell the story. 

I'm hoping a few cap changes will put it back in commission.  I'll replace any and all that's needed.  I'm unable to be in the shop this weekend through next Tuesday.  Come Wednesday, I've got some time off from the long hours, so I'll be out there early.  I will dig out some .047uf caps and have them ready.  Assuming I haven't used them all.  Not sure if RS carries these.  'Back in the day', I used to depend heavily on a Lafayette store, about an hour's drive away.  Plus, there were any number of private shops that carried everything, for their own work. 

Anyway, I'll have the parts on hand, and will post the intial results.  Thanks again, for the starting point.  Have a good one.

Jack

[Jack_Hester]

Thinking out loud, before I head back out on the boiler.  What should I expect from this Vibrato?  Compared to the favored Fenders and such?  It seems way more involved that the typical Tremolo circuit. 

Or is this true vibrato?  I am not versed well enough, in the circuits or sounds of each, to see or hear the difference(s).  I contemplated building a stand-alone Dorf Vibrato, until I started searching for the capacitors needed, that had pf values.  I haven't given up on that one.  But, it became very low priority.

Anyway, is there something really exceptional about this one, over others?  I hope so.  I'm a little off center, myself.  More concerned with it working, first, but just wondering what made Ampeg go this route.

Jack

[Jack_Hester]

I have some time off, to work on the amp.  However, my parts order has not arrived, so I've been working on the schematic cleanup.  I've got the first draft done, but I've got to do some cleanup and verification.  I'm also going to add a tube legend and voltages, when I'm done troubleshooting.  

Anyway, I've attached the first completed draft, knowing I've got to do component verification again, and doublecheck myself on the wiring.  But now, I'm working with a full schematic, and not making one.

Jack

[Tom_Hull]

capacitors anyone ,,resistors ???
the caps i needed,,,,the 8 ufs 450 volts were out of stock ,,well a short wait and the caps are in stock,,yaa...now i can finish an amp and start on an ampeg again .

http://www.justradios.com/cart.html

tom

[Jack_Hester]

Ok.  The drawing of my amp is complete.  I replaced the one in the previous post attachment.  The corrected component values verified with amp.  And, voltage chart has been added to the drawing. 

My parts order still hasn't come, so I'm going out and dig through what I have, and see if I have some .047uf caps to replace for C20, C21, & C22.  I'll look to see if I have enough to replace C18 & C19, and .1uf for C24.  If I don't have anything close, I'll wait.  Correct stuff is on the way.  More to come.  Have a good one.

Jack

[Jack_Hester]

I found three Orange Drop, .05uf-600v caps.  So, in they went for C20, C21, & C22.  I replaced C24 with another .1uf.  I warmed it up, hooked up the guitar, and strummed a chord.  Jumpered the footswitch and got a warble from the Vibrato.  But, that decayed away to none.  Lifted the jumper and put it back.  Got the warble, but again, it decayed to no warble. 

So, I'm off to start digging to see if I have a couple more caps to replace C18 & C19.  As a note: I replaced C23 with a 25uf-25v, back when I first started.  So, that one's new.  I'll be back with the results of my digging.

Jack

[Jack_Hester]

Found some .047uf caps to replace C18 & C19.  Got that done.  Got out the VTVM and warmed it up.  I have it connected the plate of V7c (pin 2).  No oscillation when I connect the jumper.  With the jumper off, voltage is a steady 250vDC.  Jumper on, steady 70vDC.  I have the Speed pot all the way down, for slowest oscillation.  I'm going to start checking resistance values (in circuit) in the oscillator.

Jack

[Tom_Hull]

hi ..jack

if it is like mine
the tremolo needs to charge up at the highest speed ..like off on mine and then turn the speed down .

just wondering about your schematic .
i just built a m12 and mine is different....

i am building another amp  an notice ther was no r 31 any where on the schematic .

did ampeg do different things for this curcuit.??.


my amp is like this .like steves 12j ampeg i beleive sort of ..

why is the r31 not on pin 2 in stead of  11,,,,,,r31 to .1 cap ..
and pin 11 directly to the first .047 cap
and the values r33 470k mine is 270 k
and 150k mine is 120k


just wondering

better to listen to steve about this

tom

[Jack_Hester]

V7c needs full B+ to operate. Check voltages on plate, grid, and cathode of V7c. If oscillating properly the plate voltage will be fluctuating at the trem frequency and will just appear erratic on most dmms. A scope or analog meter would be very nice to monitor the plate. The trem signal on the plate should be a BIG amplitude low frequency AC sine wave. You can view this signal with a scope. Or, your dmm might be able to measure it. My Fluke 87 can measure the RMS voltage as well as read the frequency of most tube trem signals.

If your V7c is not oscillating, swap V7 and V8 first, or subsitute a good tube for V7 if you have a spare. If still no go, change C20, C21, and C22 (.047µF is fine). Next check resistors in V7c circuit and measure resistance to ground for the grid and cathode.

Checked the resistors, in circuit, and they were very close to value.  

C18, 19, 20, 21, 22, 23, and 24 are all new.  Pots are correct resistances.  

So, I read back over the thread, and decided to make the tube swap (V7/V8) that Steve suggested.  There it was.  The oscillation was obvious on the VTVM needle.  Plugged up the guitar, and I have Vibrato (Tremolo?).  Though it's not very pronouced like some I've heard, it is very clear and varies with speed and intensity.  

I'm headed for the house, to see if I can put my hands on a couple more 6D10's.  Though both of these tested good on my B&K 707, the amp tells the difference.  Looks like I've got a triode that not up to snuff, on the one that is now in V8.  What was V7c is now V8c, and is downstream of Channel 1 tone stack.  

Tom -

The oscillator does not look a whole lot different from others.  But, the rest of the Vibrato is different from those that I've been studying.  And, as the amp was basically stock in it's wiring, as compared to the schematic, I will troubleshoot it as such before questioning why it's done the way that it is.  But, I appreciate you making the comparisons to those that you are familiar with.  Makes me look closer.  Anyway, I've got it working with that wiring, so it is as they intended.  Just need to see if more tube swaps will improve it.

More to come.  I love it when I'm making progress.

Jack

[Jack_Hester]

Didn't find anymore 6D10's, but found some 6AC10's.  The data sheet on the 6D10 says that its a hi-mu and used as an oscillator, and as an amplifier.  The specs on the 6AC10 says that it's hi-mu and has a higher gain than the 6D10.  But, says nothing about being used as an oscillator.  Only an amp.  

I tried it in both V7 and V8.  6AC10 in V7 and 6D10 in V8, the Vibrato does not work.  6D10 in V7 and 6AC10 in V8, the Vibrato does work, and Channel 1 sounds brighter.  With both 6D10's in V7 and V8, Channel 1 is nice and clean, but not as bright.  I swapped these two, again, and the Vibrato stopped working.  I definitely don't understand whats going on, as the triodes are obviously working.  So, I went back with the known good 6D10 in V7 and a 6AC10 in V8, for now.  I'm saving the other 6D10, and marking it 'V8 only'.

Now, to do a bit of reading about these tubes, to see if there is a substitute for the 6D10 as an oscillator.

Jack

[Jack_Hester]

Why does one triode oscillate, and another doesn't?  And, both work as amps, otherwise?  As I mentioned previously, I have my VTVM connected between the plate and signal ground, on V7c.  I noticed that the oscillation did not start right away.  Gradually, it started and then reached it's peak.  Should there be a particular type of capacitor used in this circuit? 

My parts came in the mail, today.  I believe that I'll pop the Orange Drops out, and put in the smaller physical sized caps that came in my order.  I've got to be careful of components sticking up, as the Echo tank fits into this same space. 

Anyway, I'm pondering my next move.  Unless someone has a suggestion for me to try, I'll change out C13, 14, 15, and 16.  I didn't order any .15uf caps to replace those on C10 and C12.  Just an oversight.  My goal is to see if I can get more 'Intensity' out of the circuit.  Again, it sounds good, but its like its not making a very big swing in amplitude, like I'm used to hearing with other tremolo circuits.  I'm wondering if that's because the remainder of the circuit is weak, downstream of the oscillator.  Comments much appreciated. 

Jack

[Jack_Hester]

09:35 hrs. - Heated up the pencil iron and removed the Orange Drops from C20, 21, and 22.  Replaced them with .047uf-400v polypropylene caps.  Warmed the amp up with the same tubes in V7 (6D10) and V8 (6AC10) as yesterday.  Got a nice tremolo from it.  I don't know if it's a different day, or there is a difference in the sound.  But, the tremolo sound fuller today, than yesterday.  Inspired me to swap tubes, again. 

So, with the 6AC10 in V7 and 6D10 in V8, I now have a working tremolo that I didn't have yesterday with this combination.  I did notice that the sound is not quite as bright, same as the other 6D10 in V8 (the one that wouldn't warble, yesterday).  Now, I'm inspired to give that one a try in V7.  With 6D10's in both V7 and V8, no tremolo.  So, this tube still won't oscillate.  Swapped them around, and I have tremolo.  So, I left the known oscillating 6D10 in V7, and I put the 6AC10 in V8.  Now, I have tremolo and a brighter channel.  And, this channel is brighter than Channel 2, which has octals in the front end. 

I'm hoping someone will tell me why a triode won't oscillate and another like it will.  Do you think a higher B+ will help, on that triode? 

Anyway, I'm happy with the results and the fact that I can substitute the 6AC10, if I need to.  Next up will be to do some hum cleanup, thought there's not much, except when the Echo is switched in.  Also, there is a loud pop, when switching the Echo.  I need to resolve that, too. 

And, some serious cabinet cleanup, though it won't take much.  More to come.  Have a good one.

Jack

[sluckey]

I'm hoping someone will tell me why a triode won't oscillate and another like it will.

Because one tube is a little stronger than the other.

[Jack_Hester]

Steve -

Do you see a problem with using a 6AC10 as an oscillator?  The spec sheets says that it's a bit higher gain than the 6D10, and no mention of use as an oscillator, like the sheet describes the 6D10.  It seems to work very well as one, but I like it in the amp-only position.  But, I'm thinking now that the amp is in good working order, with minor issues to cleanup, the other tubes may show signs of weakness.  Mainly because I plan for this to be an active amp, with a lot of 'on' time. 

I've got plenty of 6AC10's.  I may have some 6D10's, but I've got to dig through a lot of unsorted tubes to find them.  The 6AC10's just happened to have been sorted, and in a labeled container. 

the tremolo needs to charge up at the highest speed ..like off on mine and then turn the speed down .

Tom -

With the VTVM connected, so that I could watch the oscillation, I noticed what you stated.  With the speed pot at minimum, it took a very long time for the needle to begin to deflect and oscillate, after switching the Vibrato on.  However, with the speed pot at maximum, I got instant oscillation.  I tried this several times, with the same results.  Thanks for that info.  Something to watch for in future troubleshooting. 

Jack

[sluckey]

I think the 6D10 will be fine if you get a strong tube. I don't see any problems with the 6AC10 either.

With the speed pot at minimum, it took a very long time for the needle to begin to deflect and oscillate, after switching the Vibrato on.  However, with the speed pot at maximum, I got instant oscillation.

I did a simple mod on my recent J-12 Jet build that will take care of that slow startup issue. I highly recommend you do this mod too. It's easy to do or undo. Look at this schematic and read the conversion notes...

http://home.comcast.net/~seluckey/amps/RCA/Ampeg_J12B.pdf

Tom, this mod will work on your amp too.

[Jack_Hester]

Steve -

I wondered about that, in my Echo circuit.  Your mod grounds the output, rather than opening or completing the cathode path to ground.  My Echo circuit opens/completes the cathode path to ground, where the original circuit shows the footswitch grounding the output of the tank.  I may make the same mod to both circuits.  Thanks for the schematic and layout.  

My next move is to replace both footswitches.  Most of the time, neither will close.  I've got a hand full of momentary, but can't seem to put my hands on some maintained switches.  Maybe Radio Shack will have some. 

Jack

[Jack_Hester]

11:05 hrs. - Mods are made to Vibrato and Echo circuits.  Both cathode resistors are hard wired to the same ground as their caps.  Connecting the footswitch to ground the output of the tank works just fine.  Doing the same to ground the Intensity pot works also.  However, there is a very loud pop whenever it is grounded.  I tried connecting the footswitch to the pot wiper.  Loud pop.  I then moved it to the junction of the pot and C24.  Same loud pop.  

As a side note, before I forget to mention it, whenever the amp has been on for some extended time (like now), it pops very loudly when I put it in standby.  I'm wondering if I should put a cap across this switch.

Update - 11:30 hrs. - Changed the Vibrato footswitch back to the original configuration, and it turns on and off without a pop.  I'm thinking Ampeg had this issue, the other way.  So, they wired it in this manner.  

Now, to install new switches in the footswitch pedal.  Found a couple new ones this morning.

Jack

[sluckey]

I tried connecting the footswitch to the pot wiper.  Loud pop.

I just checked my J-12. It pops too! But my pop is not objectionable with the little 6" speaker. It is too loud when using a big speaker though. Sorry 'bout that. 

[Jack_Hester]

Steve -

Not a problem.  I had to give it a try, to make comparisons.

I just replaced both footswitches in the pedal, and now I have reliable switches. 

Any ideas of how to eliminate the loud pop when opening the Standby switch?  Other than that issue, I'm pretty well finished with this amp. 

Each channel has a open circuit jack, so there is some hum when the volume is turned up and no instrument connected.  I can plug up a guitar or microphone, and the hum disappears.  Nice quiet amp, though there's a bit of hum introduced when the Echo is turned on.  And only when the Intensity is turned up past 1/2.  And then, not very bad. 

I'm still real curious as to why Ampeg chose this configuration for their Vibrato (Tremolo).  I will make an observation about the sound, now that I've been in front of the amp for an extended period.  I have the still unresolved Falcon (Reverb hum) close by, so I can compare the two.  The Falcon Tremolo sounds just like it should.  Amplitude modulation.  The volume has a very obvious swing up and down.  I will listen to the Ampeg a little closer now, to confirm what I'm hearing in it.  But, it sounds like it has an almost chime to the resulting warble.  I hesitate to call it a ring, but maybe that's what it is.  Chime, like that of a bell, as the sound decays.  I don't know.  But, I like what I hear.  And, I've been trying to make it sound like the very pronounced Tremolo of the Falcon.  But, it's not.  Maybe it's not supposed to, with this configuration.  I hope that someone can give me a good explanation of the circuit.

Also, with the little Echo speaker cab sitting away from the amp, the sound is very clear and loud.  I think that I'll be satisfied with it, the way it is.  At some point, I'll make an adapter to be able to connect a larger speaker to the RCA jack, and see if there is any improvement. 

Jack

[Tom_Hull]

hi

nice to hear about the improvement..


tom..

[Tom_Hull]

hi
PS i forgot
i also attached the ground wire from the output transformer to the chassis so that it goes through the chassis at the far end from the grounded power tran center wire
lucky for me  a 2 inch wire instead of that long wire i had to the ground treminal...

that may have helped  my amp



i read your comment about the sound decay..
yes mine does that ,,maybe ????lol

i have a new reconed old organ tcs conn speaker turned into a guitar speaker . that holds 20 to 25 watts.
its broken in now ...and the sound is great to my ears .
John wants it . for me its mine but he can borrow it any time ..


i sorted out mine tremolo  problems all at once and it worked good after so i did not change anything..

but i put in .047 uf blackbeauties and i thought maybe its slow and all the rest because of them , i then put 3  .0047 polysteirene fast caps from an old organ , one each in  parrell to the three .047 uf caps .

and i canceled out a resistor by a parrel wire accross the resistor,,,, to the intencity ,it was 470k

my amp turn out fast and with intensity,
 any stronger and i would call it an effect pedal .

with an overdrive  vibracaster pedal hooked up,,,with the trem  off .
the amp with the tremolo on with little occilation ,, the sounds a little ear piercingly high for me ,,
so i use a volume pedal made from an lowery organ . its two long contacts that press together attached to a short small spring . which the current flows threw. my reverb tank lol

well a little less volume and that high pitch sustain calms down .
 the sustain from the tremolo  then has a decay that opens up ,,,like lol  ,,,, eeee,,, oooooo ,,,,,,lol


i had a tremolo hum and a normal umm

the humm i had was everything... i think.lol

 my guitar wiring les paule 100 ep  very poor. fixed that
the copper sheild in the guitar is there now,,
 the guitar  cable was  noisy ,changed it .
the jacks ,i put them so they could get the ground from the chassis . wrong
fixed that the jacks are isolated from the chassis now  .

the amp is almost dead silent .

there is no pop sound at all,,, when unattaching and reattaching the tremolo footswit

 hope something helps you  even though they are different amps

tom

 

[Jack_Hester]

Thanks, Tom - 

I'll sit down and digest all that you've written, when I get back from Church this afternoon. 

I need to break the amp down and haul it all to the house.  This thing is heavy, even in individual pieces.  Well, maybe not the little Echo cab.  The one thing that I haven't addressed is the cheap holding 'bracket' for the footswitch.  Two long screws and a spring stretched between them.  Is this what came from the factory?  Anyway, I'll sleeve the screws and put a new spring on with a padded sleeve.  Maybe just a flexible plastic one.  Anything will be better. 

I found a very poor dolly missing the original casters.  Lots of holes where a variety have been on it.  I found some casters that are the same specs, holes, wheels size, and just overall correct, as compared to the originals.  Unfortunately, they are shoddy offshore made.  Axle bolts put on with pliers.  I replaced those with stainless, and put thin washers between the each wheel and the metal bracket.  They cleaned up fairly well.  A shame to have to fix something new.  But, they look good.  Filled the correct holes in the dolly and put slightly oversized diameter screws back in.  The originals were #8's and I used #10's.  Can't even find original style clutch head screws.  So, I used phillips head screws.  Glad I had the other dolly as a reference.  I had to put a new attachment knob on it.  It still had the original rubber feet on it.  Cleaned up the tolex and glued the loose pieces back in place.  Doesn't look half bad.  I can see where dollies catch a beating.  This one will have a calm life for awhile. 

It's time to put the Falcon back on the bench and take a fresh look at the Reverb hum.  Such a quiet amp, otherwise.  I'll start poking around with the chopstick, and hope something rears it's ugly head.  More to come.  Have a good one. 

Jack

[sluckey]

I have a solution for the slow trem startup. I've tested this on my J12 and it works fine. Fast startup and no pops.

Refer to your schematic...

  1. Connect R30 straight to ground.
  2. Remove the ground connection from the bottom of the speed pot.
  3. Connect the bottom of the speed pot to V7c pin 3 (cathode).
  4. Connect the footswitch between ground and the junction of C21 and C22.

This is basically what Fender did in the 6Gxx series. Gives fast startup and no pop.

[Jack_Hester]

I have a solution for the slow trem startup. I've tested this on my J12 and it works fine. Fast startup and no pops.

Refer to your schematic...

  1. Connect R30 straight to ground.
  2. Remove the ground connection from the bottom of the speed pot.
  3. Connect the bottom of the speed pot to V7c pin 3 (cathode).
  4. Connect the footswitch between ground and the junction of C21 and C22.

This is basically what Fender did in the 6Gxx series. Gives fast startup and no pop.

Thank you so much.  That will be a project for the upcoming week.  I buttoned it all up, but I just couldn't take it off the bench.  

There's a little bit of hum in the Echo that keeps me thinking that it needs another look.  Nothing bad at all.  I can turn the Dimension pot all the way down, and its even less.  I'm thinking about hooking the Hum control pot directly to V7, as it seems to be common to Channel 1 pre-amp, Vibrato, and Echo.  Channel 2 is way quiet, until I enable the Echo, and turn the Dimension pot up.  I will have to revisit it all, to be positively sure of which induces the most.  Again, none of it bad.  But, the last Ampeg was quiet, no built in effects.  It has become the standard.  

I've attached my last revision 'C', which is the amp as it is now.  When I make the next mods, I will post the new one as rev 'D', to reflect these changes.  The final copy will go inside the cabinet.

I've been looking for the literature that would have come with this amp.  So far, no luck.  I was fortunate to be sent scanned copies for the last amp (B-12-N).  I compiled those into one pdf file, and those are in that amp cab. 

I'll report back with my results.  Have a good one.

Jack

[Tom_Hull]

hi

now heres is a schematic from the library.

i have no foot switch . i just have a wire grounded waiting . so and but    


on this schematic .in the trem section . can any one explain the wire to the foot switch .??

the footswitch
is it a funny switch ,,like    SPDT<< or the jack ...??

Jack does your amp have this wire ????

tom

http://www.el34world.com/charts/Schematics/files/ampeg/reverbrocket3.pdf

[sluckey]

Your footswitch is underneath R41 on that schematic.

The double footswitch for my old Gemini II was hard wired to the chassis without using any kind of jack/plug.

I did resolve the slow startup issue in my J12. The updated schematic is on my website.