Model T acting strangely...clip included

[chev]

yeah already, everything worked fine until yesterday! apart from a hum I've notice at first but didn't bother me that much.

but now it started doing this which is totally annoying!

http://soundcloud.com/chev-1/model-t-acting-out

it started doing this as soon as I remove the standby all by itself or with the guitar plug in?

it definitly needs to go see the amp doctor but hope their's nothing harmful happening when using it?

because the sound is fine while playing.

[mike_sims]

Eek! That is definitely enough to concern an owner... Can't say what it is for sure (since I'm not an amp tech) but yes, please take it in ASAP. I had a Sound City 120 before and it was making a noise similar to this, ended up needing a new transformer. But I doubt that's the case with your T... possibly a cap change is in store?

[chev]

Yeah I doubt it's a transformer because the sound & power is all there when I play...at least I hope it's not that!

and it stopped doing it after a while, like if after a good warm up it was back to normal?

But I was going to take it to the shop anyway just to make sure everything is set properly for the long run...!

[EdBass]

It's easier to determine in person rather than listening to a clip, but I think the amp is "motorboating". It could be a lot of things but is usually an issue with the power supply, a faulty capacitor, even an inductor (choke).

It could be an issue with the power transformer itself, but as is mentioned in the thread you need to get it to a pro to be sorted out.

[chev]

Yeah, I'm waiting for my friend contact, supposedly the best tech in town, has no business card, no adds or phone number, and works in the basement of a Studio...will get it there as soon as possible!

until then, I'm hopping for the best! 

[chev]

finally got my appointment for the repair this wkd.

I'll let you all know what this is all about...for the records.

[Walt-Dogg]

My money is on tubes or a component that has literally been blown to pieces by current passing through it over the years. My Ampeg V4 had a similar error, it was the death cap though or something like that, I don't recall, after that amp almost killed me I got rid of it as soon as I could haha!

[chev]

My money is on tubes or a component that has literally been blown to pieces by current passing through it over the years. My Ampeg V4 had a similar error, it was the death cap though or something like that, I don't recall, after that amp almost killed me I got rid of it as soon as I could haha!

getting rid of it is not an option for me as I've been waiting to long to get a freakin Model T! and their won't be any for a while...on my side of the border.

I wont play it until it's fix tough...at least I still have my other Sunn amps in top shape to backup!

[sunn-tanned]

Agree with the "motorboating" I have a Laney Klipp that's starting to so the same and I believe it's faulty caps...

It's easier to determine in person rather than listening to a clip, but I think the amp is "motorboating". It could be a lot of things but is usually an issue with the power supply, a faulty capacitor, even an inductor (choke).

It could be an issue with the power transformer itself, but as is mentioned in the thread you need to get it to a pro to be sorted out.

[chev]

Ok got an estimate of what's needed.
It will be a full restoration!
Full jj's tubes with KT-88, caps & bias.
So it will be louder, it's only 100w effective right now...!
Will get it back this wkd, can't wait! Haha

[EdBass]

So... what was motorboating? 

[chev]

So... what was motorboating? 

it didn't made the sound again except the one time I recorded it?

the 6550 we're close to dead and bright channel preamp tube shorted and also the bias was set to old specs
we don't know the exact cause of it but all the caps need to be replaced to make sure.

but the head is 100% original 1974 with no mods except caps and tubes.

don't know if I'll get more hints on it?

[EdBass]

Sounds like a lack of general maintenance. Like automobiles, amps need routine maintenance. Also like cars, old ones are different than new ones and used technologies from a different era.
For one example, wall voltages are higher now. Just 10% or so, but if you understand what a transformer does you know that this increase is multiplied several times before it hits the circuit, which is the reason for so many powers supply upgrade threads on this forum.
It seems that this maintenance is often ignored, and the amps often only go in for work when something breaks, and then only that specific issue is address; until something breaks again.
Expecting a "100% Original" unmaintained or updated 40 year old amp to perform well would be like driving a 1974 car for 40 years and never changing the oil, plugs, points, or adjusting the carburetor, only fixing what breaks and always wondering why it runs like crap and needs fixing all the time.


It seems that you are going for a major overhaul; good, stay on top of it! 

[chev]

yeah, the tech told me about the bias value mention in the schematic was to high for today's power so he will set it lower for a safe & longer run. he actually the info on the forum I think...hehe

the amp has been trough maintenance once already but was still setup as the 1974 specs for bias...that kills the power tubes much faster!