Results 1 to 26 of 26

Thread: 1967 Ampeg Reverberocket 2 Reverb Not Working

  1. #1
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0

    1967 Ampeg Reverberocket 2 Reverb Not Working

    Hey ya'll--

    I have an Ampeg Reverberocket 2 GS12R on my bench with a strange reverb problem. I'm sort of at my wits end, so I'm calling out for people who are familiar with these amps! I just did a recap job on it, It sounds basically like it should except the reverb has stopped working altogether. Before I opened it up there was an intermittent connection. The filter cap before the reverb was replaced with a sprague 10uf 25v, which should work just fine. All of the original caps test perfectly. Does anyone have any suggestions where I should look for an issue? It just introduces noise, sometimes reverb whistle.

    Here's a link to the schematic https://elektrotanya.com/ampeg_gs-12.../download.html

    To save some time, I know for a fact that the tank, and the 6U10 is not the problem. Thanks!

    0 Not allowed! Not allowed!

  2. #2
    Lest We Forget g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    10,429
    Thumbs Up/Down
    Received: 594/21
    Given: 1,309/5
    Quote Originally Posted by Steelwitch View Post
    The filter cap before the reverb was replaced with a sprague 10uf 25v, which should work just fine.
    Not sure which cap you mean, where is it shown on the diagram?

    0 Not allowed! Not allowed!
    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

  3. #3
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    Right next to the echo footswitch. Right after I posted this, I found a 22k resistor, which i believe is the ground for the footswitch, is totally open.. maybe I'm wrong about what it does exactly. Does anyone know? For reference, the reverb recovery is ok working. reverb drive section is not.

    0 Not allowed! Not allowed!

  4. #4
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,045
    Thumbs Up/Down
    Received: 223/1
    Given: 556/1
    That would be the cathode bypass on pin 3 of the 6U10. What happens if you lift the 20nF cap from ground off the plate of the reverb drive tube? And, I guess we're using the reverb tank's input to discharge the 470nF plate coupling cap. Do you have a scope, where you can look at the input and output of the tank drive circuit? I've NOT worked on these older Ampeg combo amps, just the current generation ones...JET's, Super Jet, Super Rocket SR212TR.

    The 22k are you referring to.....part of the grid bias network of the Reverb gain stage? You do need that 22k in the circuit to keep the grid referenced to ground.

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  5. #5
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    22k resistor replaced, but still no reverb. I know there's a lot of info about what each 1/3 of the 6U10 is doing, but do you have more info about how I can check out the input and output on a scope? I do have one, and would be useful in this instance

    0 Not allowed! Not allowed!

  6. #6
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    yes its the 22k off the grid of section 2 (Pin 7)

    0 Not allowed! Not allowed!

  7. #7
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    As I was getting voltages on the 6u10, I was getting pretty much nothing until I put a fair amount of pressure on the tube pins. I'll post voltages for each pin here in a few minutes, but it seems like the connections are very loose and this might be a case of a bad tube socket. There's a ton of RF interference. I love this amp and don't really need an FM radio.. If that is any indication of what might be wrong, I could use some advice as to why! There seems to be a grounding issue. When I was getting voltages the interference was silenced due to the grounding on the chassis through the meter.

    Edit: I redact my statement about a bad tube socket. I switch my lead to a clip and it was reading voltages just fine.

    0 Not allowed! Not allowed!
    Last edited by Steelwitch; 11-09-2018 at 01:19 AM. Reason: additional info

  8. #8
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    P1 - 59v
    P2 - 281v
    P3 - 9.6v
    P4 - 86.7v
    P5 - 147v
    P6 - 1.6v
    P7 - 288v
    P8 - unused
    P9 - 66.3v
    P10 - 284.3v
    P11 - 0v
    P12 - 57v

    0 Not allowed! Not allowed!
    Last edited by Steelwitch; 11-09-2018 at 01:19 AM.

  9. #9
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    Getting no voltage on pin 11 is pretty suspect.. Iím gonna get voltages from V5 and compare to the schematic. If anyone has any additional advice of whatís going on here some help would be welcome! Thanks yíall, as always

    0 Not allowed! Not allowed!

  10. #10
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,045
    Thumbs Up/Down
    Received: 223/1
    Given: 556/1
    You have 9.6V on the cathode KT3 (pin 3), so the grid is negative with respect to the cathode. I don't have the Ampeg Reverberocket 2 schematic here for reference, and the one you listed is too grainy to make out. So, putting the 3 stages in this order: Va Pt1 (Pin 10)=284.3V, Gt1 (Pin 9)=66.3V, Kt1 (Pin 4)=86.7V; Vb Pt2 (Pin 5)=147V, Gt2 (Pin 7)=288V, Kt2 (Pin 6)=1.6V; Vc Pt3 (Pin 2)=281V, Gt3 (Pin 11)=0V, Kt3 (Pin 3)=9.6V. So, on Va, Vg-k = -20.4V; Vb Vg-k = -286.4V; Vc, Vg-k = -9.6V. Tube section Vb looks very suspect with 286.4V between cathode and grid. Looking at the data sheet on a 6U10, the maximum ratings for the grid (with respect to cathode) voltage is 50V for any of the 3 sections. Isn't the tank driver section Vb?

    6U10-GE.pdf

    Also, with regards to the loose connections on the tube socket on this tube, can you re-tension them? On tube sockets that give you enough access, I'll use my smallest Wiha bladed screwdriver to pry them to close a bit, which usually helps. Some sockets you can't get into for doing that.

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  11. #11
    Old Timer
    Join Date
    May 2006
    Location
    Chill-Ville, VA
    Posts
    2,717
    Thumbs Up/Down
    Received: 264/4
    Given: 558/11
    nevetslab,

    It may or may not matter, bit there are 2 versions of this amp: one using a 7199 PI & 1 using a 12AX7. Also, my old 67 had a hand-drawn addition of elevated heaters on the 7591, drawn in dark pencil. As it was about 95% original I presume it came from the factory like that. Mine was the 12AX7 verdion (and came with a pair of VERY fine Amerex Bugle Boys!)

    I actually wondered if it might have been worked on by Ken Fischer himself as part of thr backlog clearing...

    Anyway, just an FYI to check both vafiations for differences.

    Justin

    0 Not allowed! Not allowed!
    "... If an older Boogie and classic Marshall had a (clearly illegitimate) child and you baked it in an oven set to clown shit crazy." - Chuck H. -
    "When receiving a shock I emit a strange loud high pitched girlish squeak." - Alex R -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

  12. #12
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Location
    Wernersville, PA
    Posts
    12,453
    Thumbs Up/Down
    Received: 181/2
    Given: 84/0
    Here is the linked schematic: Click image for larger version. 

Name:	Ampeg_GS12R.pdf 
Views:	17 
Size:	108.1 KB 
ID:	51043

    0 Not allowed! Not allowed!

  13. #13
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    The one in question has a 12ax7 PI

    0 Not allowed! Not allowed!

  14. #14
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,045
    Thumbs Up/Down
    Received: 223/1
    Given: 556/1
    Quote Originally Posted by Justin Thomas View Post
    nevetslab,

    It may or may not matter, bit there are 2 versions of this amp: one using a 7199 PI & 1 using a 12AX7. Also, my old 67 had a hand-drawn addition of elevated heaters on the 7591, drawn in dark pencil. As it was about 95% original I presume it came from the factory like that. Mine was the 12AX7 verdion (and came with a pair of VERY fine Amerex Bugle Boys!)

    I actually wondered if it might have been worked on by Ken Fischer himself as part of thr backlog clearing...

    Anyway, just an FYI to check both vafiations for differences.

    Justin
    OK, back at my shop, and pulled up both schematics of the Reverberocket. I see the one having the 1AX7 as the PI shows plate, grid and cathode voltages for the 3 6U10 tube sections that seem sensible....though on pin 11 the grid voltage MUST be a typo, it showing 250V, with the cathode at 8.6V. There's no circuit path to Pin 11 that could produce 250V. That would be 0V.

    But, looking at the tube pin readings posted, this looks like the other schematic, using the 6U10-C as the PI.

    The voltage reading for pin 7 must be wrong....288V on the grid, with 1.6V on the cathode and 147V on the plate. The schematic for this 6U10-B section shows 135V plate, 1.4V cathode, and no doubt 0V on the grid (not stated, but no source to obtain 288V, unless an internal or external connection near pin 10, where there's 284.3V.

    So, you'll need to verify Pin 7 voltage reading. If it is high like stated, there's something in the circuit area that doesn't belong.

    As for where to connect your scope probe to look at the signal going to and coming from the reverb tank (once you get the circuit voltages corrected for Section B, you can look at input to grid of 6U10 pin 11, junction of a 2.2M, 220k & 0.1uF plate coupling stage preceding this stage, then look at the connection following the 0.47uF cap off the plate of 6U10 pin 2 (6U10-A). This would be the reverb drive signal. The Return signal can be found at the wiper of the Reverb pot (when the pot is at max CW), this being from the plate of 6U10 pin 5 via 0.005uF. The Reverb signal mixes with the dry signal at the grid of V3 12AX7-pin 7.

    A quick check on the Reverb tank for DC resistance on the tank input and tank output will usually confirm the tank being ok, and not indicating an open tank xfmr coil.

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  15. #15
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,045
    Thumbs Up/Down
    Received: 223/1
    Given: 556/1
    Quote Originally Posted by Steelwitch View Post
    The one in question has a 12ax7 PI
    Same schematic I'm referring to....12AX7 is feeding the 6U10 driver (PI), that feeds the two 7591 output tubes. Anyway, read thru my post of 10:01AM minutes ago, as it refers to a problem on the 'B' section of the 6U10.

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  16. #16
    Lest We Forget g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    10,429
    Thumbs Up/Down
    Received: 594/21
    Given: 1,309/5
    Quote Originally Posted by nevetslab View Post
    So, you'll need to verify Pin 7 voltage reading. If it is high like stated, there's something in the circuit area that doesn't belong.
    Grids can sometimes not like being measured to ground. Measure with your black probe on the cathode, red to grid. Then subtract that number from what you measured from cathode to ground.

    2 Not allowed! Not allowed!
    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

  17. #17
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    Quote Originally Posted by g1 View Post
    Grids can sometimes not like being measured to ground. Measure with your black probe on the cathode, red to grid. Then subtract that number from what you measured from cathode to ground.
    I measured voltage from grid to cathode (P7 to P6) and it was reading -173vDC.. I might check with another meter just to verify. I'm not sure if it's within range of what nevetslab stated should be correct. My head is really starting to spin with this one.

    0 Not allowed! Not allowed!

  18. #18
    Senior Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    595
    Thumbs Up/Down
    Received: 338/1
    Given: 279/2
    Quote Originally Posted by Steelwitch View Post
    I measured voltage from grid to cathode (P7 to P6) and it was reading -173vDC.. I might check with another meter just to verify. I'm not sure if it's within range of what nevetslab stated should be correct. My head is really starting to spin with this one.
    With 1.6V at the cathode (P6) and 147V at the anode (P5) the tube works fine and you can be pretty sure that the grid is at 0V. Actually no need to measure grid voltage. It seems that you meter leads excite some oscillation which causes wrong readings when connected to the grid.

    2 Not allowed! Not allowed!
    - Own Opinions Only -

  19. #19
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,045
    Thumbs Up/Down
    Received: 223/1
    Given: 556/1
    Any luck with getting signal on the scope thru the Reverb Drive stage and from the Reverb Return gain stage?

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  20. #20
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    Quote Originally Posted by nevetslab View Post
    Any luck with getting signal on the scope thru the Reverb Drive stage and from the Reverb Return gain stage?
    I had to take it off the bench for a few days to get some other, more time sensitive repairs done but Iíll be updating the thread later today!

    0 Not allowed! Not allowed!

  21. #21
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    Quote Originally Posted by nevetslab View Post

    As for where to connect your scope probe to look at the signal going to and coming from the reverb tank (once you get the circuit voltages corrected for Section B, you can look at input to grid of 6U10 pin 11, junction of a 2.2M, 220k & 0.1uF plate coupling stage preceding this stage, then look at the connection following the 0.47uF cap off the plate of 6U10 pin 2 (6U10-A). This would be the reverb drive signal. The Return signal can be found at the wiper of the Reverb pot (when the pot is at max CW), this being from the plate of 6U10 pin 5 via 0.005uF. The Reverb signal mixes with the dry signal at the grid of V3 12AX7-pin 7.

    A quick check on the Reverb tank for DC resistance on the tank input and tank output will usually confirm the tank being ok, and not indicating an open tank xfmr coil.

    Ok, so input to grid of 6U10 on pin 11 is good, coupling stage off pin 11 looks good, however there is no signal across the .47 cap off of pin 2, and the signal I'm getting directly off of pin 2 looks very unstable and unclear. the return signal is perfect.

    I have switched from the internal reverb tank to a known working one. the stock reverb tank has about 200ohms on the input and nothing from tip to sleeve on the output, although I don't totally trust that it's an open transformer.. I'm starting to have buyers remorse for this Klein mm500, its not always accurate. I really need to grab myself a fluke.. anyway, it seems like this wima .47uf cap is suspect? thoughts? I gave it a quick look in circuit and it tests perfectly, but I should disconnect a leg just to double check.

    0 Not allowed! Not allowed!

  22. #22
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    weirdly enough, I just got an ampeg reverberocket r-12rt in that has the same reverb issue. 6u10 as well, I'd love to know if this is a similar problem between them

    0 Not allowed! Not allowed!

  23. #23
    Lest We Forget g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    10,429
    Thumbs Up/Down
    Received: 594/21
    Given: 1,309/5
    Any tank should read less than 1K DC resistance at the tank output jack. If it reads open it is bad, or a wire to the jack is broken.
    You said in the first post you knew ("for a fact" ) the tank was ok, so we did not second guess you. How did you determine that? Did something change?

    edit: sounds like you may just be having a meter problem, if so, ignore this post.

    1 Not allowed! Not allowed!
    Last edited by g1; Yesterday at 10:37 PM.
    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

  24. #24
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,045
    Thumbs Up/Down
    Received: 223/1
    Given: 556/1
    Quote Originally Posted by Steelwitch View Post
    Ok, so input to grid of 6U10 on pin 11 is good, coupling stage off pin 11 looks good, however there is no signal across the .47 cap off of pin 2, and the signal I'm getting directly off of pin 2 looks very unstable and unclear. the return signal is perfect.

    I have switched from the internal reverb tank to a known working one. the stock reverb tank has about 200ohms on the input and nothing from tip to sleeve on the output, although I don't totally trust that it's an open transformer.. I'm starting to have buyers remorse for this Klein mm500, its not always accurate. I really need to grab myself a fluke.. anyway, it seems like this wima .47uf cap is suspect? thoughts? I gave it a quick look in circuit and it tests perfectly, but I should disconnect a leg just to double check.
    So, input to 6U10 Pin 11 looks good & stable, output at Pin 2 is not, and no signal on the tank side of the 0.47uF cap. What happens if you unplug the input to the reverb tank? You switched tanks to use a known working tank. Are they similar in input/output impedance? In this case, are the DCR reads similar. For example, an Accutronics 4AB3C1B that we find in Fender Twin Reverbs, DCR input is less than 10 ohms (driven by small transformer by 12AU7 tube, both stages), output DCR around 250 ohms.

    The Return Signal is perfect. Meaning you can inject oscillator signal into the return circuit and all is well, or you get the reverb tank signal thru it just fine (off 6U10 Pin 5, or further down stream off the 12AX7 Pin 6, which is mixing dry with wet signal (from the tank circuit).

    I haven't had one of these amps on my bench in years. Just have the Jet's, Super Jets, Super Rockets in our inventory.

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  25. #25
    Lest We Forget g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    10,429
    Thumbs Up/Down
    Received: 594/21
    Given: 1,309/5
    Is this one of those amps with a hardwired footswitch? If there is a stuck switch or cable fault, it would ground the signal on the tank side of that .47 cap.

    0 Not allowed! Not allowed!
    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

  26. #26
    Member
    Join Date
    Nov 2018
    Posts
    25
    Thumbs Up/Down
    Received: 2/0
    Given: 0/0
    Okay yíall, Iíve learned a valuable lesson todayó I reflowed the solder on the tip and ground connections on the Reverb tank and now the reverb works! There is another present issue where the reverb trails off into feedback if itís turned up past noon. Thereís also a considerable amount of noise coming from the tank. I cleaned the RCA jacks with deoxit and the connection is good. I know these tanks tend to fail over time, but I would like to figure out if itís the tank or something else. Anyone familiar with this happening?

    1 Not allowed! Not allowed!

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Replies: 24
    Last Post: 03-30-2014, 06:55 AM
  2. 1964 ampeg reverberocket My own project weak reverb and trem not working
    By Smitty02 in forum Maintenance, Troubleshooting & Repair
    Replies: 2
    Last Post: 06-07-2012, 05:34 AM
  3. Anyone willing to help a n00b replace a PT in a working 1967 Super Reverb?
    By w302nv in forum Maintenance, Troubleshooting & Repair
    Replies: 1
    Last Post: 10-04-2010, 04:50 AM
  4. 1990's Ampeg Reverberocket 1X12 USA REVERB PROBLEM
    By loudei in forum Maintenance, Troubleshooting & Repair
    Replies: 1
    Last Post: 10-07-2009, 05:51 AM
  5. 61 Ampeg Reverberocket. weak reverb
    By retrobob in forum Vintage Amps
    Replies: 6
    Last Post: 10-27-2007, 02:18 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •