Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on January 06, 2013, 09:04:18 am
-
Got a Super Champ in yesterday that customer says in lifeless in response. I tried it and agree. The tubes seem to be OK at first look. Haven't had time to break it down and check voltages and examine the circuit. Just wondered if someone has had experiance with this amp familiar with it's issues and fixes. Got the schematic/layout off Dougs schmatics. Platefire
-
Attached is the schematic and layout. It has no circuit model/number on it. Never seen a 6C10 tube before used as a PI here.
-
6C10 is a 12 pin triple triode tube.Odd and a pain to find.
Look at stuff like preamp tube,jacks,broken resistors in the power section.Nasty amp to work on if you haven't been into one before.
-
After checking basic stuff as suggested & new/fresh tubes, I'd address the filter caps next. You could parallel them temporarily and see if it helps before replacing to save time & expense.
-
Well this is the 0lder made in USA 1980's(not the newer one) version and even though I haven't opened it yet, I think is does have a regular eyelet or turret board. The serial number is F203192 that shows a build date of 1982/1983. I think one culpret from initial test is the original speaker. I'm hearing a noise when I play that sounds like a speaker issue. A simple test though a good speaker will let me know if my ears are right but I'll do that after I've checked the circuit out first. Platefire
BTW-The reverb tank came to me loose in bottom of cab. It has a place for four screws cushioned by a plastic inserts in the tank body to kind of cushion it from the srews but no reverb tank bag? I also found the four screws laying in the bottom of the cab. Does anybody know if this thing originally took a bag or was it just srewed down uncovered to bottom of cab???
-
Voltages was pretty close:
Schematic/actual
v1a=195/200(12AX7)
v1b=200/208
v2=183/199(Reverb driver/12AT7)
v3a=260/275(6C10) Phase inverter
v3b=200/206 Driver prior to MV
v3c=200/204(reverb recovery)
v4=not listed/407(plate)
385/399(screen)
v5=not listed/408(plate)
385/399 (screen)
Bias=-33/-31.6
Heaters=6.3/6.6
6V6's and 12AX7 checked good on my TV7Au tube tester. 12AT7 Checked weak. No way to test 6C10.
Looks like everything is original including filter caps. It has an eyelet board. 1982 to 2012=30 years. Platefire
-
Plate - old filter caps that still work don't give you the same punchiness & crispness as new ones do which sounds like your original "lifeless" complaint. Everything checks out but replacing them should restore what you're lacking and wanting. You might have strings on a guitar for 5 years and they would work, reach pitch, stay in tune, but the sound would be dull & lifeless. Those things are like strings, they lose their effectiveness over time.
-
I've identified a problem I'm not sure how to address. I have a low level rumble or oscillation. At first I thought it was speaker issues but now I've got it on a known good speaker and it's still present. The amp works normal but in addition to regular amp tone this low level oscillation rumble is taking place.
I tried chop sticking the live amp last night but could not isolate one paticular thing as a source. I could tap on any part of the amp chassis, components, board and wiring and get it to start and abruptly cut off. Sometimes I would touch a paticular wire or component and it would stop/start and thought I had found it, only to find you could do that all accross the amp. Seems to be more sensitive around the power amp/bias circuits most especially on the 70uf/100V bias cap. Sometimes it went into a oscillation that resembled a more clipping tremolo vib in the low level rumble but didn't effect the guitar tone in that way, just a low level rumble noise seperate from the main guitar tone/sound.
Well guys, I would appreciate your sharing your experiance on this. I don't recall ever dealing with this paticular type problem before. On the 6C10 tube, I don't have a replacement and based on my research are very expensive. The tube performs multiple functions(gainstage/PI/verb recovery) in the amp, so I don't know if pulling it and running live would tell me anything? Platefire
-
due to the fact someone took the reverb tank loose , I would suspect that 6c10 , it's involved in the reverb recovery and the PI . I do see they are hard to find but it's very suspect . oscillation is a tough dog brother.
-
> this low level oscillation rumble
Classic sign of a 40uFd B+ filter cap gone down to 23uFd, 15uFd.... much less than the designer intended. Any unbalance in the output stage sneaks through the power rail to an earlier stage and is re-amplified.
While you could investigate (my 2 cents is on the two 20uFd), on a 30 year old amp you can bet that most of the power caps will go bad in the next few years. Once it is open, it's ten bucks to do ALL the B+ caps, that job done for many years to come. Just do it.
-
> this low level oscillation rumble
Classic sign of a 40uFd B+ filter cap gone down to 23uFd, 15uFd.... much less than the designer intended. Any unbalance in the output stage sneaks through the power rail to an earlier stage and is re-amplified.
While you could investigate (my 2 cents is on the two 20uFd), on a 30 year old amp you can bet that most of the power caps will go bad in the next few years. Once it is open, it's ten bucks to do ALL the B+ caps, that job done for many years to come. Just do it.
Maybe he'll listen to you PRR cause he sure didn't listen to me.
-
No guys, your wrong, I am listening to you and totally agree. I appreciate and value your advice. My persepective is I'm doing this for a customer that is a player that buys and sells a lot of amps. He's got more equipment than anybody I know. So I will report back to him that if he wants to make this amp a player it will need a new filter cap can and power rail resistors as a minimum and might need more after I see how it operates after the installation. Also it needs a new speaker or at least a re-cone. I tried the old fender speaker with a different amp last night and even though it works I noticed I had to turn the volume on the amp higher than normal to get a decent volume out of it plus it does have low level rattle to it along with the notes. I've been jamming on the SC over my 10" cab with a Emenance Ragin Cajun and it's sounding pretty good even as is. I think installing a NOS Westinghouse 12AT7 in place of the weak fender one helped a little. So my advice will be a minimum of new filter caps/power resistors and new speaker or re-cone to make it useable.
On the other hand if he just wants to sell it, I would recomend selling it as is because it is presently all original which seems to be important to collectors or modders. They usually want it just like it came from the fender factory. They are going for pretty high on e-bay in good shape. With a speaker recone the amp would sound pretty good as is and the next owner could bring it up to what ever they envisioned.
Again I appologize if I seem unresponsive to your advice and believe me, i'm taking eveything you say into serious consideration. Thanks, Platefire
BTW-here is some pixs
-
Couple more pixs
BTW-I went through the circuit last night and seperated a lot of wires that were up against each other to give as much seperation as possible. I think it may have helped the low level oscillation a little. Ultimate first step is new filter caps. Plate
-
Ah yes, it's beautiful inside. Add a little red sauce and dinner is served.
Brad :laugh:
-
That's a scary looking amp inside. Looks almost as bad as one of my builds. It would be interesting to see a photo progression consisting of gut shots of original Fender amps from the tweed days up through the early 80s blackface reissue days.
-
I think rivera took a handful of spaghetti and threw it at that amp and then wired it up.
Rivera-era Fenders are the worst amps I've ever seen inside for lead dress and they are way too complicated to simply get an extra gain stage.Guess he didn't have Hoffman's forum back then!
-
Yow---the wiring idea appears to be shortest run of wire between two points regardless of what you have to trod over to get there! :dontknow:
-
Sorry Plate - after reading what I wrote at midnight last night it came off sounding way harsh and wasn't meant that way.
-
Just do it.
nike amps?
--DL
-
Jojokeo
Hay! sometimes I'm due a good reaming out :laugh: Helps keep me straight!
Hay whats up DL?
-
I think rivera took a handful of spaghetti and threw it at that amp and then wired it up.
Rivera-era Fenders are the worst amps I've ever seen inside ...............
Are you sure ?
(http://www.modsbydarrel.com/national_6800_guitar_tube_amp/0%20315.jpg)
http://www.modsbydarrel.com/national_6800_guitar_tube_amp/index.html (http://www.modsbydarrel.com/national_6800_guitar_tube_amp/index.html)
:l2:
K
p.s.: Platefire Many thanks for the photo
-
Are you sure ?
Hey, that ain't fair! That's a true PTP amp. But Fender took a neat eyelet board and made it look just as bad.
-
Hey, that ain't fair! That's a true PTP amp. But Fender took a neat eyelet board and made it look just as bad.
sign that at Fender they were much better :icon_biggrin:
K
-
Hay whats up DL?
nottalotta enchilada & happy new year. :icon_biggrin:
just hacking on thermionic stuff.
work has slowed back down to a pace where i have some amp time again.
--DL
-
Yep! we always get back to personal amp time sooner or latter. I have a 5E3 head thats been in the works for two years now :dontknow:
-
notta lotta enchilada & happy new year. :icon_biggrin:
K, DL's in Texas and he's talking about just south of the boarder Mexican food.
(It's "a play on words" = "Not a lot of" enchilada. An enchilada is like an open ended calzone with sauce on top.)
Brad :laugh:
-
Thanks Brad
for your support on understanding this
effectively I can much better understand "Spaghetti Amp" than "nottalotta enchilada" :icon_biggrin:
K
p.s.: Platefire I hope you'll excuse us for the OT :worthy1:
-
My first amp was a Super Champ. After two years with it, I decided it did lots of things ok, but nothing great so I sold it. I don't really regret letting it go either. Now that I build amps, I can make stuff that sounds way better than those do and it will be made much better too....
Greg
-
I think we have just coined a new term for the worst lead dress amp "Spaghetti amps". At least I hadn't seen that term before until Physco brought it up. We seem to have drifted from Italian to mexican flavor--me ah like um both. There is a local mexican chain around her called "El Giro" I love their Salsa!!! best ever! Anyway the spaghetti amp posted above would have my vote for "The Spaghetti King Award" :worthy1: beat the Super Champ "Hands Down"
Greg-This is my first experiance with the Super Champ and I have to say I'm not impressed with it so far. It may have been kind of cutting edge in 82 for its price. I'm not being able to achive my favorite tone/response out of it yet. The amp is way too bright for me and I'm having a hard time dialing in some lows. If the customer wants me to go ahead install the filter caps in, that will help tell the tale rather the response/tone will be much improved. I need to call him and give him a situation report so he can make a call on it. Platefie
-
I'm not being able to achieve my favorite tone/response out of it yet. The amp is way too bright for me and I'm having a hard time dialing in some lows.
There's a thread or 2 in here not to long ago that's on this amp.
IIRC, Psycho, PRR, Lucky and HBP were the guy(s) fix/tune the amp.
Do a search for it, there was very good info in it.
Brad :icon_biggrin:
-
As far as I can know the "Spaghetti Amp"
is a Copyright by our friend Steve :grin:
http://www.el34world.com/Forum/index.php?topic=11389.0 (http://www.el34world.com/Forum/index.php?topic=11389.0)
K
-
Here is the Right Tool for those Spaghetti Amp
(http://www.barmanworld.com/wp-content/uploads/wpsc/product_images/Forchetta%20menu.jpg)
Those who are less experienced can also try benefit using this other tool as an help
(http://www.pinti.it/dati/CatalogoOnLine/upload/img_sub/zoom_07400001%20Cucchiaio%20tavola%20inox%2018-10%20Esclusivi.jpg)
Never try to use one of this Tools together or you'll demage your Amp
(http://www.wekeke.it/media/catalog/product/cache/2/image/9df78eab33525d08d6e5fb8d27136e95/c/o/coltelli-da-tavola-milano.jpg)
:l2:
K
p.s.: Sorry Platefire but the temptation was high
-
Well being the Super Champ is a runner up to the Spaghetti King National, it's pertanent to this thread! :icon_biggrin: :icon_biggrin:
-
Plate, I worked on one of these amps last week. The customers complaint was same as yours too much treble and very little bass. I changed a resistor and a cap in the tone stack, Slope 100k to 33k , .047 to .022(mallory) changed one coupling cap just before PI from .001 to .022(mallory), and unsoldered the bright cap on the volume pot. The customer was pleased.
Punky
-
I have a 5E3 head thats been in the works for two years now
eeek!
they're a nice sounding amp. you should finish yours. :-)
--DL
-
DL---I had just started working on the 5E3 board when the last two amp repairs came in---not complaining! I've got plenty of amps, so it can wait a little longer. I'm building it to sell anyway.
punkeykatt--If customer decides to make a player out of this amp instead of selling it, I will be proposing those mods to him. However I did find by setting the bass very high, treble very low and pulling the treble knob out to where it's a mid control, adjusting the mids helped to mellow it out a bit. Not perfect but better! Platefire
-
Greg-This is my first experiance with the Super Champ and I have to say I'm not impressed with it so far. It may have been kind of cutting edge in 82 for its price. I'm not being able to achive my favorite tone/response out of it yet. The amp is way too bright for me and I'm having a hard time dialing in some lows. If the customer wants me to go ahead install the filter caps in, that will help tell the tale rather the response/tone will be much improved. I need to call him and give him a situation report so he can make a call on it. Platefie
Yeah thats the thing with those Super CHamps...they are a good swiss army knife amp that doesn't do anything really well, so there is always something missing tonally. THey are worth a fair bit of money given what they are, but as I said, I don't miss mine at all....
Greg
-
Talked to the owner---he said go ahead with the filter caps. He said he had another 10" speaker to use in it. Mean time I will be taking a look at the old threads previouly referenced on the Super Champ to consider mod options. If you felt realy intergetic, you could always de-spaghetti it. :happy2:
Platefire
-
Closest Can I've been able to find is a CE 80/40/30/20 1 3/8"Dia x 3 1/2" long @ 525V. This is almost perfect except the CE has 30uf where the old cap has a 20uf that directly services V3B 6C10 Phase inverter. So I'm thinking this won't make enough difference to worry about as the existing cap is 80/40/20/20 450V. Platefire
-
Here is the Right Tool for those Spaghetti Amp
in addition to the 'fork' tool, make sure you keep the BFH right close to the bench.....what's a BFH? a really big hammer!
:icon_biggrin:
-
Are you sure ?
Hey, that ain't fair! That's a true PTP amp. But Fender took a neat eyelet board and made it look just as bad.
well i think i posted this one before but this is the spaghetti that's been in the corner here for years waiting for repair... (well not the one on the picture, but this model. it was designed to be used without it's OT's but combined with 800ohm speakers and runs on 11 tubes)
(http://home.planet.nl/~rneervoo/images/ag9015-2.jpg)
the fun thing is the layout in the service manual: http://soundup.ru/index.php?option=com_content&view=article&id=2657:philips-ag9015&catid=49:library-scheme-philips (http://soundup.ru/index.php?option=com_content&view=article&id=2657:philips-ag9015&catid=49:library-scheme-philips)
-
Brings back old memories! :sad2:
-
Birt I had a look to the layout on the link you posted
:l2: :l2: :l2:
That is really fun :laugh:
K
-
Are there any pre-cautions about de-soldering and soldering on a board with a pad underneath like this Super Champ? Don't think I've ever encountered the pad before. Platefire
-
Put the filter cap can & power node resistors in Friday night. Got an exact replacement of the old Mallory can by CE. Fit the same 1 3/8" hole and used the existing clamp to hold it in place. So that was the easist filter cap change out I ever done. Just disconnecting the supply wires/grounds and re-connecting them.
I fired the amp up and everything was working well but----I still noticed a low level rumble occuring as before. So now I knew it wasn't the filter caps causing it. I had already checked all the tubes on my tube tester previouly but I checked the tubes again by subbing with known good tubes. When I pulled the inside RCA 6V6 that had tested strong on my tube tester previouly and put in an old used GE 6V6, the rumbeling stopped. So it's got one RCA and one GE but sounding strong. Pretty loud, I had to turn it down, it was hurting my ears.
The amp is now operating nice and quiet. I think all it needs to operate top form in its stock condition is a new speaker and a new matched set of power tubes. The stock fender speaker sounds pitiful!!! The customer said he already had the speaker/tubes and he would install them hisself, so I guess I'm done. Platefire
-
Good job Plate.
Brad :icon_biggrin:
-
Well Thanks! I realize this is small potatoes for most of the long time builders and repair operations but I'm excited about actually getting amps to repair now that are mostly P to P on turret or eyelet boards--something I can manage. I've have been shying away from a steady stream of SS repairs request for a while now. I usually tell them I normally work on old style tube amps and haven't had a lot of experiance with SS PBC type board amps but if you can't find anybody else to work on it, I'll have a look and see what I can do!! There is always a possibility that it might be something very simple causing the problem, and I could locate it and correct it. I haven't had one call me back yet to look it over for them--but I can say I'm just being honest about it. Platefire