I agree... Plus, G&L is doing a fine job of continuing Leos work. I hope to see you in the G&L club thread.It took many years to get G&L smart though and realize Leo was only halfway there when he owned Fender.
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Ampeg repair issue, SVT-300 power amp.. advice please.
- Thread starter eyeballkid
- Start date
- Feb 12, 2006
- 61,097
- 5
- 221,257
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
If you still have the old tubes, bring them with you. Always keep and label the old tubes. I see many perfectly good tubes tossed because of incorrect or incomplete troubleshooting.
Be sure to bring everything you use with your setup so that nothing gets overlooked. Make an appointment with the tech. It's possible that something was overlooked, or there is another factor you are not seeing.
Be sure to bring everything you use with your setup so that nothing gets overlooked. Make an appointment with the tech. It's possible that something was overlooked, or there is another factor you are not seeing.
I'm in there reading all the time (took forever to catch up) but I haven't had much to add other than to announce the new arrival when I got it last year. I can see another G&L in my future at some point in time. I'm also a guitarist so that side pulls at the gear budget as well but whenever given a choice I'll always opt for the bass chair.
Whose bashing Fender? I love Fender basses. I've owned a dozen or so over the years including the modified CV PBass and Jazz Bass I have now. IMHO Leo's work at G&L was simply and extension of what he accomplished prior to that.
So while I can apologize for the diversion I make no apologies for Fender Basses or G&Ls. I play both.
I think that you need to contact the service center in writing. Then call and ask for the manager and speak to them. The entire rig needs to go back.
For your information, when a tech checks the output, they drive the input with a sine wave generator and measure the voltage at the output across a dummy load. From this the power output can be determined. They never listen to the full output through speakers. They can tell if it is clean watts by using a scope and spectrum analyzer to visualize the signal, and harmonic distortion analyzer to measure distortion. There is a spec on what the input voltage should be to drive the amp to full power, 300W in 4 ohms at a specified distortion level.
According to their reciept, they specify 37 V at 4 ohms providing 300W. V=I*R; P=VI= (V*V)/R= (37*37)/4= 342W. For reference, 34.6 volts is 300W. Maybe they are just being sloppy. There's a mistake there. I doubt that your SVT was putting out that much power at the THD spec. They don't specify what the THD was, they should have.
Your amp's user's manual spec states: less than 3% THD, 20-20 KHz, with 0.25V RMS required to drive the amp to 300W into 2 or 4 ohms. I've included the schematics and the user's manual for your amp. Early SVT-300's had a 5 ohm plate resistor on each power tube, there was a field chance to install a ferrite bead in place of the plate resistor (not in the document but the ferrite is Murata BL01RN1A1D2B or equivalent, I buy them from DigiKey). See attached service manual for the SVT II and SVT-300. This is not a big deal if you don't have it, it can help with HF oscillation and allows the amp to squeeze ot a little more.
One thing to note. The amp's level control (is this what you are calling the master?) is an attenuator at the input. Often in a preamp the Master is also an attenuator at the output. Needing to turn up the level control from normal is an indication that your preamp is not putting out the same level. This needs to be investigated. Perhaps service the preamp just to be sure.
When operating the amp, I would set the level on full and use the preamp to control the overall level. If the pre has a mater output, then you are effectively thaving wo masters in series which overcomplicates the signal pathway. Unless you are using the master/level, try setting both on full and use the preamp volume to set the overall level. See if that works for you.
Distortion and crackle can be a preamp tube. It can be a loose tube socket contact (need to retension to tighten the connection). It can be a dirty pot. It can be a dirty jack. There are other possibilities. These are things that should have been covered by the general maintenance that the the tech performed.
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^^^^^^^
This, this, and this...
I've dealt with tech's that were either bad or you basically had to do the deduction work for them.
I would take your amp and preamp with you to the tech and do a demonstration of the problem your having. I hope they can fix that amp. They are rare and a white whale of sorts. Definitely don't settle for sub-par servicing on an instrument of that magnitude.
This, this, and this...
I've dealt with tech's that were either bad or you basically had to do the deduction work for them.
I would take your amp and preamp with you to the tech and do a demonstration of the problem your having. I hope they can fix that amp. They are rare and a white whale of sorts. Definitely don't settle for sub-par servicing on an instrument of that magnitude.
I've known Bob the owner of ProTech for at least 25 years; long before they moved to the new shop.
I have never had a problem with a repair from them with the exception of a 3 Pro. They fixed a bad solder trace and it worked for a few months; same problem but it was a different trace; not their fault and I'm glad to be done with that amp.
I forget the guys name who does most of the tube repair (maybe Carlos); he is a hispanic guy who also plays bass and I've NEVER had a problem with his (or their work).
Call and ask for Jeff and calmly explain the problem.
I've played in bands with him for nearly 10 years and he as well as the rest of the company are stand up.
FWIW, I've had bad luck with EH tubes.
Wasnex knows a ton about tube amps (ask him what he paid for some used high end tubes!) and I would seek his recomendation about long lasting brands. As I recall, many here use JJ unless they wanted the primo NOS or used high end pre-amp tubes.
You could ask for a refund but they do have a bench charge as many bring in old gear in for a diagnosis and they never pick it up. That's why the front of the shop is filled with older gear (from tape decks to old Crown amps, to everything in between).
OTOH, everybody screws up once in awhile, and they certainly can not trouble shoot over the phone.
Prototypes was the only other local guy I trusted but they closed up shop some years ago. Bill was something like 80 years old and he decided to retire. The nerve....
Good luck and PM me if I can help.
I have never had a problem with a repair from them with the exception of a 3 Pro. They fixed a bad solder trace and it worked for a few months; same problem but it was a different trace; not their fault and I'm glad to be done with that amp.
I forget the guys name who does most of the tube repair (maybe Carlos); he is a hispanic guy who also plays bass and I've NEVER had a problem with his (or their work).
Call and ask for Jeff and calmly explain the problem.
I've played in bands with him for nearly 10 years and he as well as the rest of the company are stand up.
FWIW, I've had bad luck with EH tubes.
Wasnex knows a ton about tube amps (ask him what he paid for some used high end tubes!) and I would seek his recomendation about long lasting brands. As I recall, many here use JJ unless they wanted the primo NOS or used high end pre-amp tubes.
You could ask for a refund but they do have a bench charge as many bring in old gear in for a diagnosis and they never pick it up. That's why the front of the shop is filled with older gear (from tape decks to old Crown amps, to everything in between).
OTOH, everybody screws up once in awhile, and they certainly can not trouble shoot over the phone.
Prototypes was the only other local guy I trusted but they closed up shop some years ago. Bill was something like 80 years old and he decided to retire. The nerve....
Good luck and PM me if I can help.
On my D-180, it was putting out less and less output until I had to turn it up almost full and then it finally had almost no output. It was a bad screen resistor, or plate resistor I believe, but thats irrelevant.
This may sound silly, but keep playing on it and see if it gets worse. I'm no tech, but I suspect you have a component on its way out, but not totally out. Once it does go all the way out, that should make things easier to diagnose.
This may sound silly, but keep playing on it and see if it gets worse. I'm no tech, but I suspect you have a component on its way out, but not totally out. Once it does go all the way out, that should make things easier to diagnose.
That sounds like a capacitor or a wanking power supply going bad. Least you got new tubes. 
Pray it's not an internal board issue. LOL.. Doesn't seem like your tech "Really" tested it. If under warranty send it back! Force fix or replace! Just a suggestion.
Pray it's not an internal board issue. LOL.. Doesn't seem like your tech "Really" tested it. If under warranty send it back! Force fix or replace! Just a suggestion.
IMHO this is just one of many examples of sloppines on the service centers behalf. Here's another: The tech should have noted input drive level in addition to output and distortion level.
In the OP, the tech inferred a strong preamp was required to drive the amp...really? The .25V rms sensitivity rating seems pretty low for a piece of pro equipment. Noting the amount of drive required to get 300 watts would have identified if there was a problem. Either the tech doesn't know what he/she is talking about, or no effort was made to check the amp's sensitivity specs.
@beans-on-toast Thanks for the informative response. Good stuff there and I will definitely print those out to have on hand and refer to. The fella I talked to at Protech today said perhaps its an input sensitivity needing checked IF the output measurement is right. I, in my limited knowledge, are leaning more toward a failing component as its been a gradual decay and it seems like something is going amiss slowly. Im also really doubtful of the measured output. Again, the preamp functions amazingly driving ANY other amp.
@Jim C By no means am I knocking Protech. Ive taken stuff to them for years and my only complaint has been the sometimes overly long turn around times... but that happens when you're good and you're busy. I feel like they missed the mark on this one repair, but I don't think its indicative of their normal work... I'm REALLY hoping we can work out both a real repair and an agreeable resolution on the seemingly unnecessary expenses.
I called them when they opened today. They want me to bring it back and they said they will make an appointment with a tech to work on it while Im there since I have to drive so far. That's nice of them. I said I would bring my entire rig and a second tube amp to demonstrate the difference convincingly because it is dramatic. They said that's not necessary, but I told them I think it is so we can eliminate everything and they can even test the output of the preamp (which I'm sure isn't the issue), but mostly I don't want to make the drive again and leave with an amp I cant test out being told it "tested fine".
I asked about the fact that I told it was putting out 50% and needed new tubes and apparently that didn't fix it and wasn't the problem and I spent $400 bucks and they kinda brushed past that in the discussion of the amp. I dont know if the fella on the phone brushed past it on purpose or just followed the train of thought we were talking about but that's not a small issue to me, but i'm not sure at the moment if its one they are gonna want to address. We'll see, I guess. I dont mind spending $400 to maintain a great amp IF thats what is needed. I do have a problem doing that when its a waste of cash. $400 is a big chunk of change to me.
@Jim C By no means am I knocking Protech. Ive taken stuff to them for years and my only complaint has been the sometimes overly long turn around times... but that happens when you're good and you're busy. I feel like they missed the mark on this one repair, but I don't think its indicative of their normal work... I'm REALLY hoping we can work out both a real repair and an agreeable resolution on the seemingly unnecessary expenses.
I called them when they opened today. They want me to bring it back and they said they will make an appointment with a tech to work on it while Im there since I have to drive so far. That's nice of them. I said I would bring my entire rig and a second tube amp to demonstrate the difference convincingly because it is dramatic. They said that's not necessary, but I told them I think it is so we can eliminate everything and they can even test the output of the preamp (which I'm sure isn't the issue), but mostly I don't want to make the drive again and leave with an amp I cant test out being told it "tested fine".
I asked about the fact that I told it was putting out 50% and needed new tubes and apparently that didn't fix it and wasn't the problem and I spent $400 bucks and they kinda brushed past that in the discussion of the amp. I dont know if the fella on the phone brushed past it on purpose or just followed the train of thought we were talking about but that's not a small issue to me, but i'm not sure at the moment if its one they are gonna want to address. We'll see, I guess. I dont mind spending $400 to maintain a great amp IF thats what is needed. I do have a problem doing that when its a waste of cash. $400 is a big chunk of change to me.
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I can totally empathize. Before I moved here in 2012, I was thrilled to learn the area had a great tube tech. Unfortunately he moved to Nashville about a year after I arrived. Since then, if there is a problem with one of my tube amps I do the work myself.
I usually send solid state devices out for repair...I have tried a local shop a couple of times and they let me down on every occasion. I sent them three QSC PL236 amps with minor problems. They told me the circuit boards in two amps were so heat damaged that the components were falling out. I opened the amps up and couldn't find any evidence of this damage anywhere; so I apparently paid a bench fee for nothing. They are a QSC authorized service center and told me they could do component level work.
I also sent them a KT DN500+ compressor. They are not an authorized service center for KT, but said they could get schematics and should be able to do the repair with no problem. The had a junior tech tinker off and on for about two months and finally told me to come pick it up. At least they didn't charge me a bench fee on this one. I sent the compressor to Music Group and they replaced three front panel controls. Turn around was under two weeks. Music Group has provided exceptional service on two occasions now, but it involves the extra expense of parcel delivery to a distant location.
The reality is most consumer electronics is not considered economically repairable, so it's really hard for local service centers to survive and pay enough to keep good techs on staff.
- Feb 12, 2006
- 61,097
- 5
- 221,257
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Finally somebody blaming a bad cap... it was bound to happen even though it's VERY unlikely at best. Why pray that it's not an "internal board", everything on that amp is easily repaired by a QUALIFIED service tech.That sounds like a capacitor or a wanking power supply going bad. Least you got new tubes.
I don't have a lot of experience with 6550s. Most of my big bass amps are designed for KT88s. I have had really good luck with JJs. Shuguang would be my second choice. Most comparison reviews seem to prefer the sound of the JJs, but some people seem to think the Shuguangs are more reliable. I think some of the tubes vendors will be happy to advise if you tell them about your amp.
A few of my amps have shown up with EHX KT88s and 6550s. All the 6550s have failed. Most of the EHX KT88s have also failed but they drifted a lot first and then simply stopped conducting or I took them out before they did any damage. The 6550s all ran away or shorted which resulted in either burned resistors or shorted fuses. The last four bad EHX 6550s I checked with the amp on a variac. When the line voltage got up to around 110V the tubes would run away even with the bias maxed out. It appeared the tubes were less than 1 year old. I put a new set of JJ KT88s in the amp and the bias is set in the middle of the range. This is in an amp running 700V on the plates, which is just a little higher than an SVT.
I have one other amp running premium matched Sovtek KT88s. The amp sounds great, but a few months ago I checked and the bias had shifted towards the hot side and tubes were no longer current matched...basically the Sovteks are shifting around like the EHX KT88s, just not as bad.
My Skunkworks SVT is running the original Sylvanias and my Aguilar DB359 is running pre-SED Svetlanas (probably identical to Winged C). I'll try a set of JJ 6550s when the Sylvanias fail. I'll try whatever fits in the rather tight space constraints of the Aguilar...as long as it ain't EHX.
well thats not encouraging. I used to use EHXs alot when I couldnt get Winged Cs. I always like theyre tonal palette in just about any amp I tried them in. They were always pretty reliable, but it sounds like quality control has suffered since then. This was back in the days when everyone was saying their JJ's were failing left and right. Now it seems like the tide has reversed.
From what I have read, many of the New Sensor KT88 and 6550 types sound great but don't do well with high plate voltage. The SVT's plate voltage is a little lower than 700V but not much, hopefully it's low enough for reliable operation.
So far the best matching I have seen on new tubes has been from Eurotubes. I recently bought a quad of KT88s and current through each tube was exactly the same. They do a burn in before matching and give a 6 month warranty. The burn in helps eliminate bad tubes and is supposed allow the tubes to reach a point where they don't drift as much.
Before the JJs, I bought some Apex matched Shuguang EL34s from another vendor. The matching was barely within 14%. Generally 15% is considered acceptable.
Next time I buy JJ power tubes I'll be logging onto my profile at Eurotubes again. I am not a total fan boy so I will use other brands as long as there are not major reliability concerns due to the amps operation characteristics.
I checked my notes. I researched reliability of various output tube types about a year or so ago. For 6550s my comments were to consider JJ, Svetlana, and Sovtek. If I ordered from a vendor who stocked these three, I would tell them about my amp and ask straight up which tube has highest reliability with high plate voltage...FYI, The Tube Store sells all three and also the EHX 6550.
