Sunn 300t overheating

[MIJ-VI]

awesome. thanks. i think im going to call dr fretgooooood, and he's gonna make me feel allllright(sorry...i couldn't resist)


J

If I owned a soon-to-be classic tube amp, I'd want the name(s) of the very best tube tech(s) in my area, hence the thread aimed at getting this info.

There was a thread in this forum a while back listing known good repair shops, but I can't remember what it's called and can't seem to search/find it.

If/when it surfaces again I hope that it will be stickied.

 

[T-Bird]

Hi.

While the increased ventilation may sound like a good idea, without determining the cause it's a bit like running a car that has a blown head gasket with the radiator cap open.

It helps for a while and gets You to places limping, but unless the problem is rectified, more serious damage occurs. You should find the problem before trying to correct it.

Since there's only two sources of heat in a tube amp (well sometimes three), tubes and transformers (+ some resistors on some designs), either one has to be malfunctioning for the increased temperature.

The tubes heat dissipation depends on many factors, mainly the input/output power ratio and the glass surface area/power ratio and since the internals are always in the +200C range, nothing changes that.

The transformer losses heats up the transformers with about 4-10% of the power being transformed. With everything working correctly, that can not increase the heat buildup.

Babebambi has an exellent point: Did You actually measure the cabs with a multimeter to see whether they're really 8Ohm cabs?

People who say that load mismatch is OK with transformer coupled output sections (nowadays mainly tubes), are usually just parroting something that someones cousins friends brother who works for the "big boys" had heard somewhere. They usually have no idea what different functions the output transformer has in such a circuit.

The mismatch usually causes some increased heat due the decreased efficiency -> You turn it up more to compensate: Same voltage + same wattage + decreased efficiency = requires more current = more heat.

Sorry about the rant, but I'd hate see Your next thread title to be: "My Sunn 300T blew up "

Regards
Sam

 

[xjeremiahx]

Hi.

While the increased ventilation may sound like a good idea, without determining the cause it's a bit like running a car that has a blown head gasket with the radiator cap open.

It helps for a while and gets You to places limping, but unless the problem is rectified, more serious damage occurs. You should find the problem before trying to correct it.

Since there's only two sources of heat in a tube amp (well sometimes three), tubes and transformers (+ some resistors on some designs), either one has to be malfunctioning for the increased temperature.

The tubes heat dissipation depends on many factors, mainly the input/output power ratio and the glass surface area/power ratio and since the internals are always in the +200C range, nothing changes that.

The transformer losses heats up the transformers with about 4-10% of the power being transformed. With everything working correctly, that can not increase the heat buildup.

Babebambi has an exellent point: Did You actually measure the cabs with a multimeter to see whether they're really 8Ohm cabs?

People who say that load mismatch is OK with transformer coupled output sections (nowadays mainly tubes), are usually just parroting something that someones cousins friends brother who works for the "big boys" had heard somewhere. They usually have no idea what different functions the output transformer has in such a circuit.

The mismatch usually causes some increased heat due the decreased efficiency -> You turn it up more to compensate: Same voltage + same wattage + decreased efficiency = requires more current = more heat.

Sorry about the rant, but I'd hate see Your next thread title to be: "My Sunn 300T blew up "

Regards
Sam

God, if i named my next thread that...i'd be crying. i love this head. I'm going to take it in to get it checked out, just to be safe. Also, i'm trying to get rid of these cabs & just replace them with one 8 ohm or one 4 ohm cab. I did NOT test these cabs, only going off what the stickers on the back near the jacks say. I don't have the tools to test them, nor the money to buy them(at this point).

I'll keep everybody posted.

As far as fans go, should I just grab any fan & plug it in and have it clipped to the back of the amp blowing forward? Any suggestions in that field would be greaat.
thanks
J

 

[smem]

I had one of these amps and it did the same thing. What was happening is there was a problem with the stability of the bias and very gradually the bias was getting hotter and hotter. My tech figured it out and corrected it. This was an issue with the actual design, but I don't know if it was year specific or if fender ever corrected it. I don't know if this is you're issue or not, but if you get a tech to have a look, you may want to get him to have a very close look at how the bias controls are put together on this head. BTW, had no more problems after getting this fixed. Good luck.

 

[rbonner]

Your next thread title to be: "My Sunn 300T blew up

KEWL... BOB

PS. What was the original title of this thread before the Immoderater changed the name?

Ratsa-Fratsa &*%#$$$@ Amplifiers...***@@)!***& SUNN BROKEN...

I'm all for monitoring plate current and bias voltage and seeing what it does too like SMEM mentioned. I would also invest in the fan setup.

 

[xjeremiahx]

so, after a long, loud & vigorous practice today with the amp running at 4 ohms. i ran into ZERO problems. Only thing I noticed was that it ended up getting hotter quicker, but then kind of plateaued to where it normally does. I think that this may be me just getting nervous when it got hot quick without seeing if it ever got hotter than it normally does - which it didn't, it just got that hot a little quicker.

I'm still going to go and get it checked out and cleaned up & stuff when I get the cash. Wouldn't be bad to change my tubes just so I've got a fresh set in there to do the best to protect my lovely head

Thanks dudes!
J

 

[B-string]

Look in a thread called "Good amp techs" the link is in the stickies.
http://www.talkbass.com/forum/showthread.php?t=519922

 

[D.M.N.]

Kind of a month old thread, but I just thought it was worth mentioning:
I've played the Fender Bassman 300pro (darn near identical) and it got pretty hot. Not to the point of where I couldn't touch it, but to where I might not want to keep my hand there for extended periods of time. I believe the heat issue is just inherent with this amp. But if I bough one, which I plan on doing, I'd definitely get a fan or two strapped on just to keep it cooler.

 

[rodl2005]

+1 there ARE 6 6550's in there & there's NO fan installed in it stock!!! So it DOES generate a GOOD amount of heat- that AMP!!!!!! That's whay I screwed a PC fan onto the rear grate pullin hot air OUT of the amp- worked a treat!! I didn't run it into the amp(was mounted on the INSIDE of rear grate) but simply soldered a 9V adaptor SOCKET to the fan's leads & used a 9v power adaptor to plug into the fan!
Hope U get it sorted!! Can always use it to keep yr burgers warm!