Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on October 13, 2012, 01:09:25 am

Title: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 13, 2012, 01:09:25 am: Yeah Platefire's got one in over my head :dontknow: but I will give it my best shot! Hope we got some SVT Classic experts around? I easily found a manual and schematics on the net for it. I've been studying it trying to get a general understanding of how it works.

The serial number is TCLDI800007. Customer said he thinks it was made in the 90's, he bought it from a friend. He said the problem is that shortly after being poweing up it automaticly goes into "red" standby/Fault which means high voltage B+ is cut off becuse of a problem detected.

I did my first test tonight with it hooked up to a single 12" 100watt speaker. It powered up fine with stanby on. After I flipped stanby off it stayed red for a few seconds(no B+) and then went green(B+operating). I ran the amp quite a while and it never went into cutoff/Fault(red). Checking the back panel, it has two bias pots with red & green LED's over each pot to set bias with. Bias #1 controls left three tubes, bias#2 the right three tubes. Bias #2 stays green which means correct bias setting but bias #1 has the red & green stays on all the time which the manual says it is a possible bad bias control or bad tubes. I checked the tubes on my TV-7A/U and one 6550 tested bad. I re-installed with all good tubes but the red & green bias LED's stays on. So the amp seems to be running pretty good with no red plating and my guitar sound good through it. So----------

1-Not getting it to go into cutoff like customer said was a problem. Could the difference be in my 1-12 cab and his large bass speaker cab?
2-On the bias, all tubes are good covered by bias pot #1---hard to believe the bias pot is bad?

Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: LooseChange on October 13, 2012, 06:06:28 am: Did you try to set the bias with the control so that only the green was on at idle?
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: clyde on October 13, 2012, 09:51:12 am: Could this be your problem? I've had one on my bench like this.

http://johnkvintageguitars.homestead.com/SVT-VR.html (http://johnkvintageguitars.homestead.com/SVT-VR.html)
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 13, 2012, 10:58:38 am: LooseChange

Yep! I tried setting the bias. On side #1 that is showing the problem with a solid red & green(manual says "Possible bad Bias Control or bad tubes")--if you turn the bias counterclockwise the red comes on and hum increases. The manual says a solid red only is "One or more tubes not functioning".

OK-the customer gave me two new EH 6550's to use. I did find one of the existing TUNG-SOL's in the left three tubes under #1 bias with a bad reading on my TV-7A/U. I did check the EH's also and they checked good. I put the two new EH's in plus one high reading TUNG-SOL's I pulled. No change in the
in the bias readout on #1--still does what I described above.

I did try setting the #2 bias that is set at about 12:00 oclock showing a solid green(good). Hum increases if you go clockwise or counterclockwise from original position and the green light goes off but comes back when you return to 12:00. The problem side #1 is set at 12:00(same as #2) and hum increases if you go either way away from that---soundwise it's happy set same as #2. It also runs normal soundwise for my 30 minuet test at one time without going into cutoff on the standby like the customer said he was having a problem with. So according to the manual---if it's not a bad tube it's a possible bad bias control? I haven't pulled anything yet, this will be a bugger to work on. I've never seen transformers so large!! Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: HotBluePlates on October 13, 2012, 05:35:47 pm: Can you post a link to the schematic you found? Hard to know what the problem is without knowing how/why the lights indicate the way they do.

My guess is the lights turn red in an over-current situation. Lot of reasons you could have over-current, but for an average user, the safest thing to say in the manual is a tube is bad.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 13, 2012, 06:32:39 pm: HBP

Here it is in schematics and layouts in pdf:
http://www.amparchives.com/album/Ampeg/Schematics/Ampeg%20SVT-CL%20Schematics/index.html (http://www.amparchives.com/album/Ampeg/Schematics/Ampeg%20SVT-CL%20Schematics/index.html)

Here is a link to the OM:

http://www.ampeg.com/pdf/svtcl_om.pdf (http://www.ampeg.com/pdf/svtcl_om.pdf)
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: xm52 on October 13, 2012, 07:52:03 pm: This problem can occur in the CL if there is a fault in the output or bias circuit.

Something that commonly causes this is a bad screen resistor. There should be a 220 ohm, 1/2W, flameproof, 5% resistor on each screen. Older versions had a 22 ohm resistor, some had a diode in parallel. There was a technical note issued by Loud stating to remove the diode and install the 220 ohm resistor. I'd check those as well as the plate resistors.

Running the amp at a low level might not reveal the fault problem. If you have a 4 ohm 300W dummy load, it would allow you to turn it up.

Hope that this helps.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 13, 2012, 09:50:02 pm: On Drawing 075419-11 Sheet 1 of 2 Power Amp Pictorial is says:

"TO ADJUST BIAS-Allow to warm up for 20 Minutes. Adjust bias so green LEDS are lit. For unmatched tubes this condition may not be able to be met. If so adjust the LEDS so that only the red LEDS are lit.
See owners manual for troubleshooting tips using the bias controls and LEDS."

The #2 bias side on the right has three Tung Sols and are balanced with the green LED glowing.
When I play my bass through it the red LED blinks on and off with each note--according to OM, page 7, Setting Tube Bias, this is normal.

The #1 bias side has two new EH's and one old Tung Sol--not matched tubes so it is unbalanced. I adjusted the bias as indicated above where the red stays on all the time. So the red LED stays on all the time and when you play, the green blinks on as you play-according the OM, page 7, under setting the bias---this condition indicates "Tubes are not properly Matched". Well we knew that to start with on this side!

According to this everything is normal for un-matched tubes. The amp has not gone into cutoff one time with me. So the bad TONG SOL I removed may have been the problem. I do not have no large bass speaker cab to try it on and may have to let him have it back to try on his speaker cab. Also where he was playing if the voltage varies from 120VAC can cause it to go into cut off. Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: PRR on October 13, 2012, 10:45:11 pm: Bias and Fault are two separate systems, though both monitor cathode current.

Bias:

Each of six 6550 cathodes passes through a 10 ohm 2W resistor.

If *any* cathode is under 0.15V (15mA), an opamp in the left-column diverts current to the green LED.

If *any* cathode is over 0.3V (30mA), an opamp in the right-column passes current to the red LED.

The cathode currents pass through a ribbon cable. Connectors are #1 trouble-makers. Un-plug the cable. Stare and swear into each hole. Re-seat a few times. Study where the wires crimp into the connector.

Fooey on idiot-lights. Get your volt-meter on the 10 ohm resistors, one-by-one. If one tube is idling a lot hotter than the others, use a different tube. If one tube is a lot cooler than the others, try it in a different socket (a first-check against non-tube problems).

If you can get five tubes in the 15mA-30mA zone, and one at 5mA, let it be (while you save-up for a matched sextet, which the owner really should have). The idle condition is not all that critical, as long as it isn't all dead-cold or any tube over-hot.

Fault:

There's a missing detail. What is "FIL1" and "FIL2"? This biases IC2B. Diodes D49-D54 peak-detect cathode current due to signal.

Again with voltmeter on each of six 10r 2W resistor, play the *same* lick the same way and watch the voltage bump. I'm thinking, when LOUD, 300mA or 3V on 'scope, somewhat less on meter, and very nearly the same on each tube. If a tube shows no bump with signal, try it in another socket, then try another tube.

If *any* cathode current exceeds IC2B bias, a Fault is thrown. This *will* happen if the load impedance is too low and you play loud. (Check his speaker's actual impedance- don't assume the label is correct if anybody has been inside.) (Speaker "size" does not matter, though if your test-speaker is too small for 300 Watts then you can't really push it.) It will happen rarely (when loud) if one tube is loafing and the other two on that side must carry its share of the load. (Also if a tube shorts, though that's usually not re-settable.)
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: xm52 on October 13, 2012, 11:29:45 pm: I'm not a fan of their LED based bias system. The bias is supposed to be set at idle so don't be concerned what the LED's are doing when you are playing. There is nothing wrong with the system on the older amps where you measured the cathode current through a 1 ohm resistor.

One thing about any biasing, it is going to change if the line voltage changes. Some venues are notorious for having low voltage. Also some of those power conditioners can limit current into the amp.

It sounds like you are doing it properly but Ampeg has a video where they demonstrate how to set the bias on the CL:

Biasing an Ampeg SVT-CL (http://www.youtube.com/watch?v=aIHKY-OkEJs#ws)

I know it's a pain but I would still pull the power amp and inspect the resistors on the power tube board.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 14, 2012, 08:08:53 am: To be honest for sure this amp is kind of intimidating with all the bells and whistles. I saw a picture on the net where the problem with shut down was a bad cathode resistor. The picture appeared that they had both pre and power chassis standing up on end. Of course the two chssis are connected with wires, ribbon cables and then there is the fan. So problem is setting it up outside the cab to run it and check it live. Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: six el six on October 14, 2012, 11:48:23 am: I hate those amps.

The bias circuit sucks.

I hate taking them apart mostly.

The original ones were better.

I'm surprised a bo-teek builder doesn't make a 6x6550 amp that doesn't suck. You'd think there'd be a market for it.

Short rant over.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 14, 2012, 05:50:25 pm: Well this is the link I was refering to for the repair of the cathode resistor. This would probably be the way I may need to tear it down and set it up for further test. The thing is so heavy it is hard to manage but this is a pretty good window into what I would need to do--I think to check it out further. Platefire

http://www.bustedgear.com/repair_Ampeg_svt_classic_shutoff_5.html (http://www.bustedgear.com/repair_Ampeg_svt_classic_shutoff_5.html)
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: xm52 on October 14, 2012, 09:55:35 pm: These amps are very difficult to work on. They are heavy and dangerous. Some techs refuse to work on them because it costs more to service them. A set of umbilical cables to extend the connections helps. Otherwise you have a precarious balancing act.

In case this helps, the two trios of the push pull pair are the three on the left, the left bias pot adjusts them, and the three on the right, adjusted by the bias pot on the right. Some people mistakenly assume that the pairs are the three in front and the three in the back.

The problem very well could be the 10 ohm resistors as you indicated. It could be the 220 ohm 6550A screen resistors, or it could be 8 and 14 pin DIP chips on the power board. These are the most common sources of this problem.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: HotBluePlates on October 14, 2012, 11:34:08 pm: Quote from: six el six on October 14, 2012, 11:48:23 am
I'm surprised a bo-teek builder doesn't make a 6x6550 amp that doesn't suck. You'd think there'd be a market for it.

You can find original SVTs out there, and every bass player I know that has an amp over 100-150w uses a solid state amp. Small and light, cheaper to buy and use.

And I notice many bass players that want "tube color" are using much less power, along the lines of a B15N.

Anyway, it seems a slim market, all things considered, and the owners of the Ampeg name also bring you Crate goodness. :sad2:
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 15, 2012, 02:10:55 pm: Hay Guys, thanks for disscussion and input on this. Please examine my reasoning! I see no reason digging into this beast unless it's absolutly nessesary. Throughout my playing over it the last week I have not got it to go in shut down mode not even once! Automatic shutdown was the problem the customer noted.

The amp when I got it has 6 TONG SOLS that I assume was a matched set when new. The #1 bias pot side had both LEDS lit that according to the manual indicates "Both on all the time=Possible bad bias control or bad tubes. The #2 bias pot side was lit green that according to the manual indicates "No Problem"

OK, I checked the 3 tubes with my TV-7/AU Tube tester from the #1 bias side and found one tube with way below minimum reading. I replaced that tube with one of the new EH 6550 the customer provided. This sets up an almost automtic mis match of tubes for side #1.

According to the previouly referenced schematic note that says, "if you have an mis-matched tube combination set the bias where the red LED remains lit". This is what I did on bias control #1 with the replaced EH tube.

So right now as I play my bass over the amp and observe the LEDS, on the #2 side with no problem with green LED, when I play a note the green remains on and red come on also and back off with each note(normal for matched tubes). On the #1 side with the new tube, the red LED stays on and the green comes on also and back off with each note. According to the manual "Red Comes on,then green=Tubes not properly matched" (normal for mis-matched tubes).

So I'm thinking if I get him try it on his speaker cab and it no longer goes into shutdown, he just needs to get a matched set on tubes to stay in the green. If it goes into shuddown, it needs to be opened up and the problem found/corrected. Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: phsyconoodler on October 15, 2012, 02:30:05 pm: Hey Plate,
After fixing many of those amps,you are dead on with your assessment.They absolutely have to have a matched sextet of tubes for the bias led's to both be in the green.
Your reading of the manual is correct in that you have one side biased in the red with mis-matched tubes.
They do blow the little 220 ohm resistors a lot on those amps,but if the amp is working and sounding good it is unlileley they are blown.
It is really easy to change them once you know how.
Those amps are expensive to re-tube and guys who own them need to be prepared for the costs involved.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 15, 2012, 09:59:13 pm: Hello phsyco

Thanks for the confirmation! I will let him take it back and try it and if all is well, he'll just need to invest in a new matched set of tubes. If not!!! I'm glad you confessed to having hands on experiance so I will know who's bell to ring if it comes back :icon_biggrin:

His dad has a 1966 Dual Showman head he wants me to work on. That will be more in my league than the Ampeg. But if it does come back, I will tackle it--very carefully! Platefire

BTW:also thank you PRR for the detailed explination provided. It is appreciated and helped my understanding of the fault & LEDS bias systems. It will also be a good reference should it come back and I really have to dig into it.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: PRR on October 15, 2012, 10:40:33 pm: What I'm thinking.....

A four-engine airplane with just one idiot light for temperature.

Real 4-engine planes have four temperature gauges.

For another buck they cudda gave you a dozen LEDs, two per _tube_. Maybe not on back, but inside where the technician goes.

Yeah, the "off bias" LEDs are correct for a non-matched set. I would prefer no red (over 30mA) LEDs, but the manual says that's OK. Set it free and see if it comes back.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: phsyconoodler on October 16, 2012, 12:10:45 am: Led's are for computers. They should have bias ports for each tube so you can plug a meter into each one.AND....they should have individual bias adjustments for each tube too.
THEN....they would have a great amp.
Oh,and one more thing.....They should not be made in Vietnam!!! What an insult to Americans!
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 16, 2012, 02:09:31 pm: Well I decided I would do one more test before I gave it back to the customer to try. I took the tubes
out of bias side #2 and installed them is bias side #1 and vice versa. Guess what! the LEDS didn't change---same readout. So I think this indicates the problem is not in the tubes. In adjusting the bias pots the LEDS are operating as follows:

1-Amp is quietest with both pots set to 12:00 Oclock. In this condition Bias #1 LEDS green and red stay on continuously. Bias #2 is green continuosly.

2-Turn Bias #1 counterclockwise from 12:00, red stays on continuously hum get louder the further counterclockwise you go. Turn pot clockwise from 12:00 green and red stays on continuously with hum getting louder the further you go clockwise.

3-Turn Bias #2 counterclockwise from 12:00 both LEDS go out and hum gets louder the further you go counterclockwise. Turn pot clockwise from 12:00 green and red stays on continuously with hum getting louder the further you go clockwise.

Platefire

s
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: PRR on October 18, 2012, 12:00:14 am: Don't bias by hum.

Since the problem does not follow the tubes, go back to the 10 ohm cathode resistors, screen resistors, *and* that unreliable ribbon cable.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: plexi50 on October 18, 2012, 06:50:22 am: Miss matched 6550's is what i have found on more than one occasion. A mother to get chassis out on the bench and as heavy as my van
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 18, 2012, 10:21:54 am: Har! I called two music companys about 80 miles away north-Shreveport Music, South- Red River Music Alexandria La trying to get a POC name/numer of their repair Tech in order to try to find someone local with experiance with this amp I could refer the customer to(other than me). Shreveport Music would not give the contact info of their Tech and said if they worked on that amp they would start with a new set of matched tubes plus what ever else would be required and would probably be a minimum of $600.00. Red River Music would not also give me Tech contact info and said it would be a $70.00 bench fee plus what ever else parts and labor required.

I don't have a shop or bench to work off of and with the complications with the big and bulkeyness plus the technical complications I'm inclined to bow out. You could actually do more damage to this amp taking the 2 chassis out of the cab and let things get away from you letting it fall and pull something loose or break. The only way I will work on it if he fully understands that this is beyond my level of experiance and I'm flying by the seat of my pants and couldn't be responsible for other damage cause by doing that. Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 18, 2012, 12:50:50 pm: Right after I made the previous post I heard from the customer and I informed him of all I tried so far including my reservations about working on it as mentioned in the previous post.

I found out he does have two large cabs to use with this amp. I think one with 8-10 and another with 2-12/4-10 or something like that. He said the problem occured when he was playing with his band and noticed a big flash(supposably from the tubes) coming from the back of his amp and then went into shutdown. I don't know if he tired some different tubes or what but at some point he tried it again and the same flashing/shut down event happened. He said after that the amp would go into shut down almost immediatly after he turned it on. Of course I never got it to do that over my 1-12 cab.

He is going to talk it over with his Musician Dad and determine if he wants me to work on it. I figure if I'm going to be open to amp repairs to more modern type amps I've got to get my feet wet at some point. I keep getting calls for SS and hybred amps and have turned them down so far---this amp is just a tough one to start with!! :icon_biggrin: Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: xm52 on October 18, 2012, 02:36:44 pm: It's amazing how clients forget to mention things like lightning coming from the back of the amp.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Willabe on October 18, 2012, 02:41:24 pm: Quote from: xm52 on October 18, 2012, 02:36:44 pm

It's amazing how clients forget to mention things like lightning coming from the back of the amp.

:w2:

Brad :l2:
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: plexi50 on October 18, 2012, 04:53:19 pm: Quote from: xm52 on October 18, 2012, 02:36:44 pm

It's amazing how clients forget to mention things like lightning coming from the back of the amp.
:l2:
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: PRR on October 19, 2012, 01:03:26 am: > I don't have a shop or bench

Oh, hell no ! ! !

It *might* clear-up with a matched sextet.

But you can't be sure it doesn't have other problems which will come back to bite you.

To be sure, you need to take it apart and spread it out.

I work on a 2,000 pound Miata, a 4,000 pound minivan, and a plowtruck that runs 8,000 pounds with plow and ballast. The Miata, I just turn it up (with a jack) and poke. The minivan is harder. The plowtruck is a %$#@! to work on. (Even stuff on top, because it's so tall.)

You need a BIG STRONG bench and significant special jigs and rigs to work on a SVT.

Drag it to the porch and tell him to get it before someone breaks their neck on it.

You should get reasonable per-hour for the time you spent, even if no certain good came of it.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 19, 2012, 09:40:45 am: OK, that's it. I'm not going to work on this amp. I appreciate all the input. Looks like we had to go through all this jyration to get to this bottom line. Proverbs 24:6 and in a multitude of counsellors there is safety

Thanks, Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Willabe on October 19, 2012, 09:48:11 am: The best hitters don't swing at every pitch that comes across the plate.

OTOH, I am a Cubs fan. :laugh:

Brad :icon_biggrin:
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: John on October 19, 2012, 10:42:04 am: Quote
OTOH, I am a Cubs fan.

Now THAT'S dedication!!
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Willabe on October 19, 2012, 10:44:45 am: Yeah, tell me about it.

Brad :l4:
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: gldtp99 on October 19, 2012, 02:46:48 pm: Plate--- i have no problem refusing to work on SVT's or any other amp job i don't want to mess with---if i even think the job might be over my head, i refer the people to the local pro techs---they're good at what they do and are set up for jobs like this.
The other day a guy who bought one of my PA head re-builds (happy customer) asked me to come down the hall, in the band rehearsal building we share, to "look at something".
We go into a band room and there is the band with a rack system with a VHT tube power amp---the guy tells me that one side of the power amp is inop and the other side is lacking power, and would i take a look at it ?
Now over the last yr or so, several people (studio techs, etc) have asked me to fix this particular VHT--- and I've always told them to tell the band to take it to the local pro tech---now after all this time, they still haven't taken it over to the pro----- why ?
Maybe:
1) They have "bad blood" with the local pro techs and aren't welcome there anymore---- non payment/PITA customer ? I've run into this before.
2) They don't have the $$$ to pay a pro tech---then why should they have $$ to pay me ?
3) They run the amp into the dirt until it is inop and expect me to wave a magic wand over it to restore it to 100% operation for @$20 ?
4) Expect that if I attempt to service this unit, then i'm responsible for anything that ever happens to it in the future (I've run into this, too)

I try to avoid "no win" situations and limit myself to amp work that i'm comfortable with and people that I'm comfortable to have as customers---- My limited bench time is also an important consideration.
Don't be afraid to refuse to work on any piece of equipment if you don't feel confidant that the job will end up being a positive experience for both parties----refer it to the pro techs, that's what they're there for---they should have the training, experience, and equipment to handle jobs like this---- it's how they make their living, and i don't want to deny them their livelihood--- I'll do the occasional re-tube/re-cap/general service on some vintage amps, from outside customers, but most of the time I'll refer jobs to the guys who do this for a living--- i support the amps that i build/rebuild but only one has had anything other than a re-tube in over 8 yrs---a bad PT that i replaced for free and loaned the guy a BF Showman until the part order came in...................................................gldtp99
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: smackoj on October 19, 2012, 06:26:29 pm: I read this thread with a lot of interest....mechanical as well as philosophical....really 'bitchin'

Curt Granger in Birmingham AL builds a 300 watt tube thumper now....don't know if it's better than the one senor Platte has just danced with, but his Plexi repros are top of the heap IMHO.

Here is a link if anyone wants to snoop around down in Birmingham? http://www.grangeramp.com/sbva-300.php (http://www.grangeramp.com/sbva-300.php)
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: plexi50 on October 19, 2012, 08:47:40 pm: Dont give up yet. I know how heavy and gouging they are on the hands and arms (cuts and bleeding) but in the end you will have beaten that SOB. Thats what makes you never forget that monster. There is no doubt that working on the old and newer SVT are a mother. I myself just cant let any amp beat me though. I know that when i take an SVT on it is going to kick my azz 9 times out of 10. It's all part of being a non conformist and rebel to me. But you also need to know when to hold them and when to fold them. There is no shame in simply getting an amp that is more trouble than it is worth. Especially one that has factory flaws and just poor build quality. Amps like that will make you insane and it turns out to be one thing after another. I have one now that has all rusted pot shaft nuts that was evidently in a saltwater environment. I have to cut the nuts off with a dremel and expand them open on one side to get then free of the EQ. All pots are shot and the amp was just plain disrespected it's entire life. This is a hell situation but i got to do it*
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 19, 2012, 10:05:14 pm: Well that's the thing hardest for me is, I'm not a quitter. Usually no matter how tough things get I believe in seeing it through. In this case the sheer weight of this head is massive and is not too terrible to handle in the cab but I know when that power amp chassis is pulled out it will be akward to handle. You would just about have to use the transformers as handles to manage it. In my case not having a shop area I don't have a good place reassemble the chassis/cables for hot testing outside the cab especially vertically(standing up on end). To heavy for the kitchen table to low on the floor. Don't seem like you would want to depend on it being balanced in that position(vertically) but you would need something to secure it in that position. Probably what PRR ment by using a jig. Then there is the issue of the electronics, board and the extra high B+. I haven't yet attempted to pull the chassis yet so IMHO if you are going to bail out, this is the time to do it. So in this case I will bail.
It's really strange because opening an old amp up that is old style P to P, turret board or eyelet board to me is fun as eating cake and ice cream and I'm completely at home. I know to progress or modernize I need to move into PCB board maintenance/experiance but don't think the SVT is a good place to start. However I have worked on a couple of PCB's. I am planning on buying a storage building in the future and plan to create a shop area in that. If your going to service amps is pretty much a "must have". Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: PRR on October 20, 2012, 11:57:21 pm: > Too heavy for the kitchen table too low on the floor

Right. You need a "transmission bench", sturdy enuff to hold a car gearbox at wrench-level with some blocks so you can turn it over to wrench the bottom without it rolling off and crushing your dog.

The SVT is slightly lighter than a T-10, but more fragile, and needs different blocking. (Also preferably a bench not soaked in gear oils!)

> I'm not a quitter.

OTOH, if you don't have some basic work-support, you are not really a 'player'.

WWJD? Not Jesus, but his 'dad' Joseph The Carpenter. Carpenters have benches. Joe lived a long time, supported a family, surely he had whatever bench suited his work. OTOH, Joe did live a long time, and so will you. Perhaps times when his bench was minimal and he would only whittle door-latches. Perhaps times when he hewed massive timbers on a huge stump.

Joe would also have these thoughts:

> don't have the $$$ to pay a pro tech---then why should they have $$ to pay me ?
> expect me to wave a magic wand over it to restore it to 100% operation for @$20 ?
> i'm responsible for anything that ever happens to it in the future

Some jobs are not worth doing. Or perhaps, as we say here: "That job's not ripe yet!" I have jobs on hold until I get proper benches.

And the thought that major investment in an SVT-strength bench just may never pay-off. Maybe after this you will only see Champs and Kays.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 21, 2012, 06:40:13 am: Amen!
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: xm52 on October 21, 2012, 09:36:21 am: You have be comfortable with any job that you take on. Having the proper workspace and tools are a must. The last thing that you want to do is cause more harm than good, both to the amp but most importantly to yourself.

I've been zapped a few times and figure that I've been very lucky. Knowing when and when not to stick your hands into an amp is a good thing. Assuming you live through the electrocution, you avoid an ambulance ride to the hospital and being put on a heart monitor to make sure that your heart doesn't decide to stop some time later. Those sort of fun things. Very serious stuff to say the least. This applies to any amp. A small Fender can kill you just as easily as an SVT. A big heavy cumbersome chassis does increase your chances of making a boneheaded move.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on October 21, 2012, 10:10:37 pm: Well this guy has got another imported SVT that he got when this one became unreliable. This SVT I got of his is USA made. He said the new imported one don't sound as good as the USA one did. So I guess he has high regard for this amp even though presently disabled. His Dad got my number from another local guy that I've successfully repaired several of his vintage amps and called me regarding the SVT of his Sons and also his 1966 Dual Showman. I was mostly interested in the Showman repair but thought how hard could the SVT be :BangHead:

Their thought is that both are tube amps and I work on tube amps. Last conversation with him I did explain the differnce in old tube amp electronics, and new and my hesitation to work on it. Considering his high regard for this USA SVT and knowing my circumstances, it's only right that I refuse to work on it and recomend he take it to a professional Tech. I may loose the Showman job over that, but that's OK. I can walk away knowing I did the right thing in this circumstance. My stress level is also much improved!! :l2: Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: TubeGeek on October 22, 2012, 12:46:25 am: That's the problem...SVT's cause stress and lot's of it. I have accepted thus far 4 svt's in for repair and although each one has ended up as a successful job, it was a very stressful ride. Each time I was in the middle of the job I'd be cussing at the stupid amp and I swearing I was never going to accept another one! Lone behold I say yes to them when I get the calls cause I enjoy a challenge (sometimes).

At this point I think I'd also pass on the job. The last thing you want is to dive in and have an oopsie moment and then you're in it for the long haul. That feeling definitely isn't a good one. I think most of us have been there.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: six el six on October 22, 2012, 01:52:54 am: I feel your pain and have definitely been there.

The 1970s era SVT I don't mind. They're simple.

The new ones though?! Major PITA every damn time.
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on November 23, 2012, 09:58:06 am: I just got a new AMS catalog in the mail. The SVT CL head is $2,200.00! I knew the head was expensive but had no idea---that expensive. I play bass pretty decently but by no means a pro but
for me if I was going to play bass live I would just buy a good SS amp---clean clear bottom at a lot less expense and weight. Platefire
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: gldtp99 on November 23, 2012, 03:23:17 pm: I agree--- there are some very good ss bass heads out there---- sometimes I get people asking me to build them a high powered tube bass head--- usually after their bandmate gets a tube guitar head from me--- I tell them to get the best solid state bass head they can afford and usually have to go into a long explaination of how impractical a 1000 watt tube bass head would be.
i don't want to even bother with a 300 watt tube amp----- i'll leave these builds to others--- i don't want to go over @500V and use expensive to source PT's to push big bottle tubes to higher wattages.
12 to 50 watters are what i'm most comfortable with---- but I'll do a 100 watter from time to time if needed---- just finishing up an EL34 x 6 Sound City 120-to-Hiwatt conversion (the last one i'll be doing).
I've been playing some smaller builds at home lately---- a high gain 14/7 watter set on the 7 watt position and a 10 watt Newcomb PA/Fender 5E3 conversion--- both thru a 1x12 cab--- lots of great tone and great fun---and my ears don't ring afterwards...........................gldtp99
Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Platefire on November 23, 2012, 04:12:14 pm: I had a request to build a tube bass amp from an old bass playing friend about a year ago. I didn't agree to build it at the time but told him I would research the idea since I hadn't ever build a bass amp. In fact I think I started a tread on the subject and the SVT came up as a recomendation. I never got back with him becasue I really didn't want to build it. I've talked with him since then and he never brought the subject up and I didn't either. I really have an opinion that the function of bass guitar amplification is what SS is best suited for and I guess that is why I can't wrap myself around the idea of building a bass amp. I would have to get over that hump to put myself into it. Platefire

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Title: Re: Got a Ampeg SVT Classic in For Repair-----Heeeeelp!
Post by: Ritchie200 on November 24, 2012, 06:51:00 pm: No shame, be safe!
Jim

Eastwood- A Man's Got to Know his Limitations (http://www.youtube.com/watch?v=_VrFV5r8cs0#ws)