Need some help tuning my unstable wreck please

[Richie]

you may have to try quite a few different preamp tubes in V1 position..

you should be able to turn all controls wide open,and bright switch on..and the amp not squeal.. [no guitar plugged in]

[declan]

declan, I remember that thread...I'm ChickenLover on TGP.

Afternoon (or good morning in Florida) Fischerman/Chickenlover, i dont post too often on TGP, can never find my post again if i do

funny , you mentioned that thread here about a day after i read it on TGP so it was an easy find.

im just counting the hours to band practice to see how she sounds before making any more changes.

Here are her guts in another thread

https://tubeamparchive.com/viewtopic.php?t=5430

[Fischerman]

I took a glance and you might want to look at the grid wires for the power tubes. The plate wire for the second PI triode (very end of preamp board) comes fairly close to those grid wires. Possible source there.

Then also look where you have that brown OT wire going over both grid wires. Another source there.

And try to keep the NFB wire away from everything.

I also noticed your treble wire and another wire are very close but that may not be a problem.

A quick and dirty way to locate the source of oscillation is to put a .01uF cap across the plate load resistor for the stage you want to check. That cap will very often cure the oscillation and then you have a better idea where to look. Then you can remove the cap and try to fix it. Lots of high-gain amps have these caps in parallel with the plate load resistors to increase stability, decrease hiss, and sometimes for tonal reasons (lops off the highest of the highs). So there's nothing wrong with leaving it in there if you like it.

[declan]

thanks fischerman, good to have a quick diagnosis on the actual patient, i will report back on how the surgery goes

[geetarpicker]

Neither my original or two clones of it have any squeal issues. However my original did have a squeal issue long ago and the fix was a little piece of foam rubber wedged under the edge of the PS board to keep the output transformer primary leads pushed down against the chassis. You might check the placement of those wires but it could be other lead dress issues.

[geetarpicker]

Double post deleted

[declan]

Rooster with the guitar vol on minimum or unplugged and everything up full with full bright there is just a hiss now, no squeal. i think that 47pf cap is the answer

Glen those tips for amp and head placement were very useful. Singing sustain when standing a few feet away, but in front of the head, changing to beautiful scream when i point the pups twoard the cab. the first note would last forever if i stayed there.

its now singing like that pretty much all over the neck, i can still feel her instability, those strings have to be dampened when not playing and if you get the PUPs pointing the wrong direction too close to the cab or head she starts to snarl at you. I will try the foam under the PS board Glen, it seems pretty easily reversible

The highs can still be a little piercing at times, but I dont want to loose where she is now so i am going to be careful with any changes from now on.

these amps really are on the edge, she spat Mullards in V1 back at me and demanded a Brimar..... i understand now why Ken gave his trainwrecks womens names nasty and beautiful all at the same time

I still cant help myself, ive got to find out what some chopstick surgery will do, but i did much more playing than tweaking tonight, Practice with the band tomorrow night will be interesting

[rooster]

Woah - Thank all of you for checking in here for my benifit as well as declan's. I got so much input and it was all worth while, THANK YOU!!

As to my squeal thing, it turns out to be the first preamp tube. And I have to say that this is really madening because it pretty good example of a Tungsram, something I know that Ken liked here. The signal just ramps up so high! As I jack the Treble and Mid knobs up along with the Volume knob, you can hear the tube start to go and then the little squeal starts. Well, I guess I should be more specific here - it is more like a high pitched whistle than a squeal, if you know what I mean. Have you all been on this page? Please tell me 'yes'!!!!!!!!!!

I did add the 47pf cap and it made no difference obviously - because the trouble was something else - but I do imagine this cap contributes to the stability of the amp so I will leave it. Thanks for the push....

Right now I am done for the night but I will reinstall a resistor at V1, on the input side just to see how it impacts the whistle noise. I suspect a whistling tube is a whistling tube, but I kind of want to see if it - the resistor - actually alters thing and how much. Richie, I know you make these amps for a few people, and Glen, I know you need to have yours working their best, too. Tell me then, what tubes are you using in V1? Declan mentioned the Brimar, OK, what else? The thing is, there will never come a day when I turn all the knobs to '10', so, in so many ways, I can get by with tubes that are not PERFECT. Still, I would appreciate some direction if you wouldn't mind? Thanks!

One last concern that I want to address regarding tubes and these amps. With a mindset of performing with one of these amps, #1 question: How many backup tubes do you guys travel with, and 2: Is it common/typical for the circuit to tax a good example of a great preamp tube well before its time? If you are going to tell me that a truly great version of a tube has a lifespan of 25% of what it might have in another amp, I would love to know this. If you tell me that a truly great tube will last for years in here like it will in other amps, then I would like to know this, too.

FWIW, I am pulling very good examples of working NOS tubes from my other amps and finding that they are not so good in the Express. Haha, I thought it was hard to find a decent tube for my Super Reverb V1!!!!!!!! That is a frik'n cake walk!!! Thanks to all!! YOU ROCK!!!

[Richie]

It doesn't matter what tube brand etc.. you have to go through some and see if they will work. And yes it does take a bit of time trying them..

If you have a tube you say is not perfect.. you could still use it, for your own amp,just find one that doesn't squeal at the setting you normally play at.

You also have to fine a tube that sounds good, so once you find one that doesn't squeal, then you have to listen for the tone of the tube.

One way i might suggest, is to contact terry Kilgore [sarge overdrive aka tubetramp], he pre screens the tubes..so when you get one, it should work in the wreck.. Just tell him the tube is for a wreck preamp.

A little more expensive..but he sells good tubes.. Much easier than buying a pig in a poke, or 10 of them only to find they might only work in a lower gain amp.

Richie

[rooster]

Richie - Yeah, I saw an article about him in Vintage Guitar Mag I think. Anyway, I cannot come up with an address for him from google that is not a porn site. Do you have a contact method? Thanks.

One thing about his article that totally freaked me out was that he insisted that a Marshall Plexi sounded its best when the power tubes were very mismatched. I mean he was saying 30-40mas out if I remember right. (!!!!!!!!) It was a two or three part series and this was his closer. ??? Tone is tone I guess, but can tell you I won't be trying this anytime soon.

But I would like to try a V1 from him, sure, and thanks.

[Richie]

http://mhuss.com/sgtoverdrive/

I think the article was edited and some things were not correct.. or misquoted.. I could be wrong, but seems i remember something about that..

[declan]

At practice levels, which were two clicks down on the airbrake she is back to some feedback and howling, so its time for chopstick surgery, the PI cap only took her so far, still some taming of the beast to be done.

Our other guitarist likes the top end and it does work well in the mix, his only complaint was she needed more agression so i guess its also time to try those 5200 taps and see how she sounds with our distortion loving singer/guitarist.

where do you guys put your spare taps, I just had a thought that mine are coiled up under the PS board .... could this also be a cause of the squealing feedback

[jjman]

Richie - Yeah, I saw an article about him in Vintage Guitar Mag I think. Anyway, I cannot come up with an address for him from google that is not a porn site. Do you have a contact method? Thanks.

One thing about his article that totally freaked me out was that he insisted that a Marshall Plexi sounded its best when the power tubes were very mismatched. I mean he was saying 30-40mas out if I remember right. (!!!!!!!!) It was a two or three part series and this was his closer. ??? Tone is tone I guess, but can tell you I won't be trying this anytime soon.

But I would like to try a V1 from him, sure, and thanks.

There were several things stated in that series of VG articles that were questionable. VGM has not been covering in depth technical aspects of amps until more recently and I don't think they were using the same fact-checking vigilance they would have if those 3 articles were about guitars.

All who mentioned dealing with Terry said he is great and knows his stuff.

[rooster]

Ritchie - Terry did check in and I will pick up some tubes from him. THANK YOU!! He was talking some strange voodoo in his email but he did get to the subject at hand. All of which is to say he has a good sense of humor and he also leaves me with a feeling of confidence in the purchase. Yes, this is a cat who knows tubes...

declan? To you especially and to everybody else, I do want to ask a question regarding the load resistor on V2. Is everybody with a stable amp using 150K - or something less? I have seen and heard conversations on this site where people are talking values as low as 33K. Ritchie, can you share this info? Too,Ritchie, are you using the ToneSluts power trannies?

declan, what I do is pull those taps up to the top of the chassis, cap them with heatshrink, and bundle and tie them so that they sit to the base of the OT. I think to drop them into the chassis area is just asking for some other parasitic opportunity. Besides, the interior of the Express is too tight already, eh?

[Richie]

He was talking some strange voodoo in his email but he did get to the subject at hand. All of which is to say he has a good sense of humor and he also leaves me with a feeling of confidence in the purchase. Yes, this is a cat who knows tubes...

Yes Terry has a lingo all his own, and sometimes if you don't know his writing, it may be hard to figure out.. And he is funny. But he does know his tubes.

Yes i use the 150k resistor.. that resistor along with the cap has a frequency.. if you change the value of resistor, then you'll need to chage the cap to get the same or close frequency of that section. I think there is a chart here, that some have done the math on.

Whatever tap you use.. heat shrink off each unused wire [tap] and leave them under the power board. The ones i know i'm not going to use, i cut them off to about 4"

I've tried and used many different transformers. The toneslut trannys are a good set of trannys, and i don't think you can go wrong with those.. But i use a different set. I've used NOS Stancor trannys and Pacific. And some different Heyboers..