Help troubleshooting a Bogen conversion gone wrong - Telecaster Guitar Forum
The Number 1 Fender Telecaster Guitar authority in the world.
   

Go Back   Telecaster Guitar Forum > The DIY Channel > Shock Brother's DIY Amps
Forgot Username/Password? Join Us!

Shock Brother's DIY Amps Building or modding your amp? Then use this forum to discuss the process and show your pride and joy.


Wilde Pickups by Bill & Becky Lawrence WD Music Products Amplified Parts Mod Kits DIY Amps, Mods, Pedals dallenpickups.com Warmoth.com seymourduncan.com


Forum Jump


Reply
 
Thread Tools
Old December 11th, 2012, 03:37 AM   #1 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
Help troubleshooting a Bogen conversion gone wrong

I've been working on fixing up a Bogen H30 PA head. It worked when I got it, but sounded weak, and obviously hadn't been touched in decades. So, today I replaced the cap cans with individual electolytics, replaced most of the other caps, some of the resistors, put in switching input jacks, and speaker out. Tubes are 3x6SF5, 6SL7 phase inverter, 2x6L6G, 5U4G. All brand new or NOS except the rectifier at this point. I tested it every step along the way, and it progressively sounded worse. Very depressing...
Here is the photofact. Schematic is first :

http://www.whiteghostshivers.com/ima...k/79-5-004.jpg
http://www.whiteghostshivers.com/ima...k/79-5-003.jpg
http://www.whiteghostshivers.com/ima...k/79-5-002.jpg
Now it motorboats for a few seconds, then sounds incredibly harsh, and max volume is soft. If that's not bad enough, R33 continues to smoke and burn up, with all tubes in. This is obviously a symptom, so I'm hoping you all can point me in the right direction of possible causes.
With all tubes but the rectifier pulled, I'm getting 520VDC on the plates, and B+ around 480V. When all tubes are in, I can't leave it on for more than a minute without R33 smoking. Iron is a monster in this amp, schematic values are 420VDC plates. I say this because while the voltage is high with no tubes, my PT and rectifier seem OK.
The stock R33 started smoking as soon as I installed the new 5uf filter caps, but I seem to be getting proper B+ at every node, that is until R33 smokes and everything goes to hell. Thoughts?


Last edited by smokebreak; December 11th, 2012 at 04:17 AM.
smokebreak is offline   Reply With Quote

Old December 11th, 2012, 05:55 AM   #2 (permalink)
Friend of Leo's
 
Telenut62's Avatar
 
Join Date: Oct 2008
Location: Eugowra, Australia
Age: 54
Posts: 4,494
First thing I'd look at.....is the R33 resistor going to ground. Are the 5uf caps polarised...+ - and facing the right way.

Interesting set up with the M2 switch
__________________
.....I love the sound of distortion in the morning!!
Telenut62 is online now   Reply With Quote

Old December 11th, 2012, 06:50 AM   #3 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
Quote:
Originally Posted by Telenut62 View Post
First thing I'd look at.....is the R33 resistor going to ground. Are the 5uf caps polarised...+ - and facing the right way.

Interesting set up with the M2 switch
No joke. R33 looks to be in the path of a strange FB loop. 5uf caps are facing the right way, though I must admit I turned the amp on with all of them backwards for about 10 sec in my haste to get it goin. I very well could have destroyed something, thought it takes about the same time to warm up, so I'm hopeful. There was no dramatic failure, and R33 is not going to ground
smokebreak is offline   Reply With Quote

Sponsored Links   #
Sponsored posting
 

Old December 11th, 2012, 09:54 AM   #4 (permalink)
Tele-Holic
 
CraigB's Avatar
 
Join Date: Nov 2009
Location: Central Coast of CA
Age: 51
Posts: 731
Are you attempting to restore this amp, or as the title of the thread denotes, convert it to a guitar amp?

That network is not necessary, unless for some reason you need the 500R tap. Remove C17, C18 and R33.

You can test your electrolytics to see if they are functioning properly.

1. Set your meter to high volts DC, black probe on (-), red probe on (+) on suspect cap. If there's voltage present that hasn't bled off yet, you should be able to watch it slowly bleed down on your multimeter.

2. If there's no voltage present, set your meter to continuity and place one probe on (+) and one on (-). (Seriously, make sure caps have been discharged before you do this, or you could screw your meter). You may hear a very brief beep from the meter, but if it keeps beeping, the cap's no good. Do not proceed to the next step. Replace damaged cap.

3. Assuming beep is very brief or none at all, remove probes, set to high volts DC range, power the amp up and place red probe on (+) and black probe on (-). You should see the cap at full B+ in short order. Turn amp off with probes still in place (obviously, it helps to have clips on your probes when you're doing things like this) and you should be able to watch the cap slowly discharge.

Be aware that caps can explode and the electrolytic spewing out can burn you. The least protection would be safety glasses and a long sleeve shirt, but a face shield is better.

CraigB is offline   Reply With Quote

Old December 11th, 2012, 02:23 PM   #5 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
I'm trying to restore it first, then either change the values in the switch network to work like FAC, or possibly just take it out and put in a tone stack. I'll test out the PS caps, but I'm already on my second build with that section. I started with 2x10uf and 4x5uf, and now trying 10,10,8,8 in the decoupling section with no success.
smokebreak is offline   Reply With Quote

Old December 11th, 2012, 06:27 PM   #6 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
caps are charging on powerup, and discharging on powerdown. I'm getting voltages everywhere I should. I'm baffled. I have now replaced every cap in there, and now it's worse. I get no guitar signal out of the speaker, and a contsant bupbupbupbup . Logically speaking, the motorboating started right after I replaced the 4x5uf capcan with the individual 4.7's. Here is a picture of the guts before I touched it:
http://www.whiteghostshivers.com/ima...n%20wiring.jpg
note the underside of the capcan(brown). there are 4 positive terminals, and starting with the one at 10oclock and going clockwise, they correspond to B+ nodes 1,2,4,3, in that order(i think, as I traced it from schematic). only 2 of the neg terminals were in use, and all go to ground. the ground lug is the blob to the lower left of the capcan.
Here is the amp as of now :
http://www.whiteghostshivers.com/ima...k/p9150199.jpg
please excuse the mess...this is the second rebuild of the PS so i paid no mind to prettiness...just trying to get it going.
all i can think is that i don't have the caps in right, and i'm hoping some extra eyes will unearth a simple mistake. thanks for the help thusfar.
smokebreak is offline   Reply With Quote

Old December 11th, 2012, 06:28 PM   #7 (permalink)
Tele-Holic
 
CraigB's Avatar
 
Join Date: Nov 2009
Location: Central Coast of CA
Age: 51
Posts: 731
Cool, sounds like a fun project. All you really need on the OT secondary is the 4/8/16 taps. You can remove C17, C18 & R33 on the 500R tap, and remove wire between C17 and R20. The schematic shows it as a separate secondary altogether. Remeber to check and see iff all voltage is drained off caps before working on it.

While you're at it, set your ohm meter to the lowest setting and check OT plates to center tap and see how much DC resistance you get between the leads. So, for instance, using a hypothetical number of 150R between pin 3 of V5 and OT center tap, you should get roughly the same reading between pin 3 of V6 and center tap, and ~300R between pin 3 of both power tubes.

You should also be able to read a very very small amount of resistance between 4, 8 and 16R taps to ground.



If you're still getting weak sound (and you're certain all tubes are good) could be a few different things. Off the top of my head without any notes in front of me (at work, slow day) here's a list of things I routinely do when servicing an amp:

1) Clean and tension power tube sockets. For cleaning, I use a castaway bad tube, or tube base, spray cleaner on the pins, insert and withdraw from the socket a couple of times. Wipe off spray cleaner residue.

2) Clean preamp tube sockets same way.

3) Clean scratchy sounding pots - remove from the chassis to do this. Spray a few good shots of cleaner in the shell and work the taper a few times back and forth. Repeat. If you have a compressor or can of compressed air, blow cleaner residue off, and wipe off outer shell, shaft and terminals with a lint-free clean cloth. Be careful not to blow the cleaner residue back in your face!

4) Check each ground connection visually and with multimeter, making sure there's a good solid (no resistance=continuity) connection to ground.

5) Check resistor values, ballpark +/-10% should be OK. Any resistor that's drifted more than about +/-20% could make a difference - replace.

6) A close visual inspection, looking for any bad/cracked/cold solder joints, burnt resistors or blistered coupling caps. (Use magnifying glass or OptiVisor)

7) Replace ALL electrolytic caps.

8) Replace all coupling caps.

9) Blow out chassis after working on it with compressed air, or clean with shop vac. (I like compressed air better)

That's all I can think of right now.

Good luck, let us know how it goes.
CraigB is offline   Reply With Quote

Old December 11th, 2012, 06:42 PM   #8 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
Quote:
Originally Posted by CraigB View Post
Cool, sounds like a fun project. All you really need on the OT secondary is the 4/8/16 taps. You can remove C17, C18 & R33 on the 500R tap, and remove wire between C17 and R20. The schematic shows it as a separate secondary altogether. Remeber to check and see iff all voltage is drained off caps before working on it.

While you're at it, set your ohm meter to the lowest setting and check OT plates to center tap and see how much DC resistance you get between the leads. So, for instance, using a hypothetical number of 150R between pin 3 of V5 and OT center tap, you should get roughly the same reading between pin 3 of V6 and center tap, and ~300R between pin 3 of both power tubes.

You should also be able to read a very very small amount of resistance between 4, 8 and 16R taps to ground.



If you're still getting weak sound (and you're certain all tubes are good) could be a few different things. Off the top of my head without any notes in front of me (at work, slow day) here's a list of things I routinely do when servicing an amp:

1) Clean and tension power tube sockets. For cleaning, I use a castaway bad tube, or tube base, spray cleaner on the pins, insert and withdraw from the socket a couple of times. Wipe off spray cleaner residue.

2) Clean preamp tube sockets same way.

3) Clean scratchy sounding pots - remove from the chassis to do this. Spray a few good shots of cleaner in the shell and work the taper a few times back and forth. Repeat. If you have a compressor or can of compressed air, blow cleaner residue off, and wipe off outer shell, shaft and terminals with a lint-free clean cloth. Be careful not to blow the cleaner residue back in your face!

4) Check each ground connection visually and with multimeter, making sure there's a good solid (no resistance=continuity) connection to ground.

5) Check resistor values, ballpark +/-10% should be OK. Any resistor that's drifted more than about +/-20% could make a difference - replace.

6) A close visual inspection, looking for any bad/cracked/cold solder joints, burnt resistors or blistered coupling caps. (Use magnifying glass or OptiVisor)

7) Replace ALL electrolytic caps.

8) Replace all coupling caps.

9) Blow out chassis after working on it with compressed air, or clean with shop vac. (I like compressed air better)

That's all I can think of right now.

Good luck, let us know how it goes.
Thanks a bunch. I think we were posting at the same time...there's my update above your post. I've swapped out tubes to no avail...pulling the PI is the only thing that stops the boating. I did remove the components in the 500ohm tap section, and at least nothing is smoking now ;) Obviously the underlying problem is still there though...
smokebreak is offline   Reply With Quote

Old December 11th, 2012, 09:00 PM   #9 (permalink)
TDPRI Member
 
Join Date: Dec 2012
Location: Florida's Space Coast
Posts: 5
(deleted, posted in error)
Reprobate is offline   Reply With Quote

Old December 11th, 2012, 11:38 PM   #10 (permalink)
Banned
Tele-Holic
 
Join Date: Jan 2011
Location: Belle Plaine, KS
Posts: 610
"In an amplifier that has ever worked correctly once, motorboating is almost always a signal that the decoupling capacitors in the B+ lines of the preamp section are going high impedance, not decoupling properly. Replace the B+ decoupling capacitors at least for the preamp. Since the other capacitors are old, also, consider replacing ALL of the electrolytic capacitors in the amp (doing a cap job - see the Tube Amp FAQ at http://www.eden.com/~keen for info on the what and why of cap jobs.)"

straight from the geofex tube amp debugging page, which you should have read before starting any tube amp project ever.
TheSmokingMan is offline   Reply With Quote

Old December 12th, 2012, 04:13 AM   #11 (permalink)
Tele-Afflicted
 
Join Date: Jun 2010
Location: Homesick Texan in Maryland
Age: 69
Posts: 1,292
Deleted; posted in error.
__________________
John

Pictures of musical instruments are very much like sculptures of food.

Last edited by syrynx; December 12th, 2012 at 04:35 AM. Reason: Posted in error
syrynx is offline   Reply With Quote

Old December 12th, 2012, 10:42 AM   #12 (permalink)
Tele-Holic
 
CraigB's Avatar
 
Join Date: Nov 2009
Location: Central Coast of CA
Age: 51
Posts: 731
Ahh, PTP, so fun to troubleshoot If you've heard the term "divide and conquer" it applies even more so when working on these things. Break the circuit down into modules, if you will, and address each module separately, test with your meter, and check it off your "list". It's like the "100-point inspection" you hear about when buying a used car from the dealer.

One thing I forgot to add to that list, which is something I do when building my own amps, not necessarily servicing an old one.

Print your schematic and take a highlighter pen and mark EACH ground point. Now with your meter set to continuity checker, systematically verify that each and every ground point gives a good solid beep, no resistance reading. Sometimes my meter will show a tiny reading, but anything more than an ohm or two or a different reading than all the rest of your ground points may be a problem.

Another note: I've seen those kind of pots on old hifi equipment - if you look closely, the solder terminals are extremely close to the surface of the chassis. If they get distorted or mangled in the process of working on it, you could be grounding out there. It's also quite easy to break the connection between the terminal and the taper if you really hank on that sucker.

You should remove the pot, use a solder sucker to clean the terminals, then straigten them up and use your meter set to ohms to test for proper operation. When resintalling, add another lock washer or flat washer to get those terminals spaced away from the chassis. While you have them out, give 'em a good shot of DeOxit or at least some compressed air.

If damaged, replace.

And most definitely, thoroughly clean out the little bits of wire strand and solder before powering up. A good blast of compressed air or shop vac cleaning is in order here.
CraigB is offline   Reply With Quote

Old December 13th, 2012, 01:38 PM   #13 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
Quote:
Originally Posted by CraigB View Post
Ahh, PTP, so fun to troubleshoot If you've heard the term "divide and conquer" it applies even more so when working on these things. Break the circuit down into modules, if you will, and address each module separately, test with your meter, and check it off your "list". It's like the "100-point inspection" you hear about when buying a used car from the dealer.

One thing I forgot to add to that list, which is something I do when building my own amps, not necessarily servicing an old one.

Print your schematic and take a highlighter pen and mark EACH ground point. Now with your meter set to continuity checker, systematically verify that each and every ground point gives a good solid beep, no resistance reading. Sometimes my meter will show a tiny reading, but anything more than an ohm or two or a different reading than all the rest of your ground points may be a problem.

Another note: I've seen those kind of pots on old hifi equipment - if you look closely, the solder terminals are extremely close to the surface of the chassis. If they get distorted or mangled in the process of working on it, you could be grounding out there. It's also quite easy to break the connection between the terminal and the taper if you really hank on that sucker.

You should remove the pot, use a solder sucker to clean the terminals, then straigten them up and use your meter set to ohms to test for proper operation. When resintalling, add another lock washer or flat washer to get those terminals spaced away from the chassis. While you have them out, give 'em a good shot of DeOxit or at least some compressed air.

If damaged, replace.

And most definitely, thoroughly clean out the little bits of wire strand and solder before powering up. A good blast of compressed air or shop vac cleaning is in order here.
Thanks Craig! After going section by section, I found :
- R2 wiper was reading to ground, as it shouldn't
- I had connected C12 to the cathode of V4, instead of to r18 in the switch network
-While I though I had removed the 500tap network as suggested, I hadn't removed the wire from R20 to C17

So it looks to me as if C12 was causing my problem(500tap network may have been fine and not burning up R33 if I had wired it up correctly in the first place). I'm still a bit unsure about what was happening in the circuit, in technical terms, when I had C12 wired incorrectly. Also, I first got C12 in the right spot, with no change in the symptoms. It was only after I snipped the wire run from R20 to the 500tap that all was cured. Theres a lot of things at play here, but I'd love to hear a description of why these particular miswirings were causing my symptoms.

I got the chassis mostly cleaned out, and am going to go in and redo my patch and splice job, remove the switch circuit in it's entirety, and put in its' place a Baxandall on concentric pots. At least that's the plan. Once I bang on it for a while, I may sub some coupling caps out too, as this thing was obviously not intended for guitar. It is however, very loud now, which makes me happy.

Oh on a side note, i upped the FC to 10ufx2, then 10,10,8,8, as opposed to the schem 8ufx2, 5ufX4. I only have the sound of the amp when I first got it to compare, which seemed a bit weak due to the old caps, but I'm thinking upping the values has made the amp have more of a tightness to it.

Cheers, Jeremy
smokebreak is offline   Reply With Quote

Old December 13th, 2012, 10:45 PM   #14 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
This amp is starting to warm up to me : https://soundcloud.com/jeremyslemend...r-bogen-h30-pa
I changed the 1st coupling cap from .02uf to .005, added a .01 bypass cap to the grid resistor to 2nd stage, and changed cathode bypass on 2nd stage from .003 to 25uf. I've since changed that to .68 and it gets real clean and nice but like Fender bright switch-probably great at the club but very annoying to my neighbors. I haven't put a tone stack in yet, I figured I'd get close then see about attenuation. Pardon the shiity Iphone recording and cheap Weber test speaker. I'll make some proper clips once I get it right.
For those still learning the basics, like me, this tutorial really helps : http://www.regiscoyne.com/tech/preamp_mods/
smokebreak is offline   Reply With Quote

Old December 14th, 2012, 01:55 AM   #15 (permalink)
Tele-Holic
 
CraigB's Avatar
 
Join Date: Nov 2009
Location: Central Coast of CA
Age: 51
Posts: 731
Sounds pretty good as is. Nice pickin too Jeremy Get that filter cap board mounted on standoffs and have fun modding it!
CraigB is offline   Reply With Quote

Old December 14th, 2012, 02:35 AM   #16 (permalink)
Friend of Leo's
 
Telenut62's Avatar
 
Join Date: Oct 2008
Location: Eugowra, Australia
Age: 54
Posts: 4,494
Why do you need a tone stack? lol
If you look at other 6V6/6L6 circuits you'll work out some other bits you don't need, nice twanging by the way
__________________
.....I love the sound of distortion in the morning!!
Telenut62 is online now   Reply With Quote

Old December 14th, 2012, 05:56 PM   #17 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
Quote:
Originally Posted by CraigB View Post
Sounds pretty good as is. Nice pickin too Jeremy Get that filter cap board mounted on standoffs and have fun modding it!
That was the first thing I did yesterday :) there was an existing hole right there so it was quite convenient!
smokebreak is offline   Reply With Quote

Old December 14th, 2012, 06:07 PM   #18 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
Quote:
Originally Posted by Telenut62 View Post
Why do you need a tone stack? lol
If you look at other 6V6/6L6 circuits you'll work out some other bits you don't need, nice twanging by the way
That's a good point. I never even considered not having a stack of some sort but now I see how I can just dial it with caps and resistors. I'm still amazed that last night(clip) it sounded somewhere between a Vibrolux and Masco (to my ears)and today it sounds like a twin, just by changing the cathode bypass. When I got the amp there had been a mod done probably decades ago, as there was a 100uf cap in the .003 schematic spot on the cathode! I think i'll put a bunch of caps on a rotary.
smokebreak is offline   Reply With Quote

Old December 14th, 2012, 10:25 PM   #19 (permalink)
Tele-Holic
 
CraigB's Avatar
 
Join Date: Nov 2009
Location: Central Coast of CA
Age: 51
Posts: 731
Quote:
Originally Posted by smokebreak View Post
That's a good point. I never even considered not having a stack of some sort but now I see how I can just dial it with caps and resistors. I'm still amazed that last night(clip) it sounded somewhere between a Vibrolux and Masco (to my ears)and today it sounds like a twin, just by changing the cathode bypass. When I got the amp there had been a mod done probably decades ago, as there was a 100uf cap in the .003 schematic spot on the cathode! I think i'll put a bunch of caps on a rotary.
As long as you can turn the switch and get good sounds with all your different guitars, why not leave it? If any settings are not useable at all, you could play around with modding there. It sounds good dude! Congrats. I love those old Bogens. I could've bought a mint one for $40 back when I first started building/modding, but I passed on it because I didn't want to hack it into a guitar amp. Little did I know I could've just restored like you did and had a cool guitar amp...Oh well
CraigB is offline   Reply With Quote

Old December 15th, 2012, 02:26 PM   #20 (permalink)
Tele-Meister
 
smokebreak's Avatar
 
Join Date: Jul 2011
Location: Austin, TX
Posts: 110
Thanks Craig. I'm thinking I may put the cathode bypasses on a spdt, and then an FAC type rotary between the plate of V3 and the grid of V4a. That could be fun? Speaking of fun, I'm kinda torn between leaving well enough alone, or using this amp as a sort of modding playground, in the effort of learning. Soooo...that said, I've got an used preamp tube in V2. I'm thinking about cascading that into V1, so that input one would be as is, and input 2 would have an extra gain stage. So can I just connect R9 to the grid of V1? What other factors do I need to consider if I were to go this route? Up the value of R9? I'm just not sure if I would be upsetting bias, if I haven't already
smokebreak is offline   Reply With Quote

Reply

Bookmarks

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

/td>

» Random Photo for Guests
74 Tele
Untitled Document



 


Powered by vBadvanced CMPS v3.2.2



IMPORTANT:Treat everyone here with respect, no matter how difficult! No sex, drug, political, religion or hate discussion permitted here.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.6.0 RC 2
© TDPRI.COM 1999 - 2014 All rights reserved.