102 Feedback City

[talbany]

Great looking house Tony!

Congrats!

Thanks T..Now I have to haul all that Sh&^t back upstairs before the wife gets back!!

T

[ToneMerc]

Great looking house Tony!

Congrats!

Thanks T..Now I have to haul all that Sh&^t back upstairs before the wife gets back!!

T

Tony, that's just another reason to "clone" that amp.

Mike

[jelle]

Yes, an invisible one..

[brentm]

nice music room

Yeah!!. I wish..My ass is above the garage Wife insisted we use it as a sitting room..You know the room your wife spends all your money buying nice stuff for and you never sit in it.. Just got the place so far diggin it!!..Richmond Va..
Gil Where the hell is Blair Witch!!

Tony

Ah, I had that argument once. My vote was for my pool table, but we got a "formal living room" instead. I still take issue with paying for part of a house I didn't use but once or twice a year.... but I can understand that a pool table sends the wrong message when company comes over.

Interesting results with your amp and the long cable. There is definitely something going on there! Hopefully it can be uncovered and (hopefully) then repeatable.

[mlp-mx6]

Tony - unrelated, but I lived in the West End of Richmond, working at Circuit City's HQ for about 10 years. We lived off Hungary Road, near Staples Mill - used the Gaskins Road exit off 64. I also lived in an apt. off Hull St. Rd. and Chippenham for a while. What part of town are you living in? How is Richmond these days? I miss the restaurants there. Great town.

[Colossal]

Oh yeah I heard of the movie. Never saw it though..I didn't know it was filmed in Fredrick County..I just came from Maryland (St Charles Co)y

Tony, do yourself a favor and never see that movie. You'll be really pissed and demand an hour and a half of your life back. Great looking house!

I probably missed it in this thread, but what transformers did you use for your build?

Thanks.

[CHIP]

Nice home Tony. We enclosed our porch last year with the same type windows. Looks very similar to your room.
I would also like to thank you for sharing your efforts with trying to crack this feedback situation. It's very interesting and helpful.

[talbany]

but I can understand that a pool table sends the wrong message when company comes over.

Brentm.. I see my wifes point to!!Bunch of amps and stuff in the first room you see when you walk in.. I think I have her talked into a nice Baby grand and maybe my 102...Wish me luck!!

Tony - unrelated, but I lived in the West End of Richmond, working at Circuit City's HQ for about 10 years. We lived off Hungary Road, near Staples Mill - used the Gaskins Road exit off 64. I also lived in an apt. off Hull St. Rd. and Chippenham for a while. What part of town are you living in? How is Richmond these days? I miss the restaurants there. Great town.

My place is in Hanover Co.. Mechanicsville It is a bit on the rural side for me growing up in the DC area..Gets pretty quiet back here.. The wife and I like to hang down in Shokoslip quite a bit Yes the restaurants here are wonderfu.. The Morten's here makes killer steaks!!..I also get to see my Friend Lindy Fralin often..So far so good!!

I probably missed it in this thread, but what transformers did you use for your build?

The Iron I used was a Heybor Twin/Showman.. PT Mojo (I believe) The OT I got from Eric (a member here) It's a NOS never been used 100w Bassman 4ohm sec..Hope this helps!!

I would also like to thank you for sharing your efforts with trying to crack this feedback situation. It's very interesting and helpful.

Unfortunately I wasn't much help discovering why the amp behaves like this..I am going to keep at it and hopefully find some more clues.. Since I have another one of Erics OT I am going to attempt to replicate the feedback in another build and see if I get the same results..
I'll try and keep everyone posted..
Thanks to all for listening and the great FEEDBACK!!

Tony

[greiswig]

I swear I remember somebody suggesting that Tony plug the pre output into a different amp to see if the amp still behaved the same way, which I thought was a really interesting idea. I just skimmed this thread again for the first time in 2 weeks, and didn't see...Tony, did you do that?

[LeftyStrat]

I swear I remember somebody suggesting that Tony plug the pre output into a different amp to see if the amp still behaved the same way, which I thought was a really interesting idea. I just skimmed this thread again for the first time in 2 weeks, and didn't see...Tony, did you do that?

Honestly, and I seem to be in the minority here, I believe it is the PS filtering. Anybody with a 102 clone just needs to replace the PS supply with 50uf to see if it makes a difference.

[sonicmojo]

I swear I remember somebody suggesting that Tony plug the pre output into a different amp to see if the amp still behaved the same way, which I thought was a really interesting idea. I just skimmed this thread again for the first time in 2 weeks, and didn't see...Tony, did you do that?

Honestly, and I seem to be in the minority here, I believe it is the PS filtering. Anybody with a 102 clone just needs to replace the PS supply with 50uf to see if it makes a difference.

That doesn't seem to compute since Tony sent the preamp out to a different amp with similar results. I don't have a 102 but I tried exactly that in my Bluesmaster and it didn't affect things. My two 3rd gens are standard with 50uF and I also pushed all of them up to higher bias with 30W tubes. I personally think it is something different happening in his amp (or a combination of many things). But I don't have a 102. That may be next on my list!

[wokkel]

Because you can get feedback on the clean side, things around V1 seem to be key.

But to establish this a bit further, would you be so kind and replace the V1, V2 (and perhaps) V3 tubes with similar, or more run-off-the-mill tubes.

If you replace only one tube, is the feedback disappearing with only V1 replaced?

Harald

[talbany]

I swear I remember somebody suggesting that Tony plug the pre output into a different amp to see if the amp still behaved the same way, which I thought was a really interesting idea. I just skimmed this thread again for the first time in 2 weeks, and didn't see...Tony, did you do that?

g.. I did run the pre out into my Music Man 100w and there was no mistaken it was there.. My Music Man has 160uf on plates and 20uf on screens...It's definitely in the pre amp

Several here have tried going 50uf on the plates in there amps and didn't notice too much change..

The amp originally had the newer blue TVA's.. I thought it might have been in the filtering as well so I changed them out to the older Yellow TVA's on the screens PI and V1 and found no difference..So it's NOT in the filter caps themselves

Since it is going on in V1 clean as well this is where we believe it is coming from..BUT HOW!!..This is the Mystery!!... Since the OD is grounded in clean we can eliminate and cross coupling going on from the OD side..

Since the tone stack is out of phase with the input it's hard to believe there is any cross coupling going on there as well..

Because you can get feedback on the clean side, things around V1 seem to be key.

But to establish this a bit further, would you be so kind and replace the V1, V2 (and perhaps) V3 tubes with similar, or more run-off-the-mill tubes.

If you replace only one tube, is the feedback disappearing with only V1 replaced?

Harald

Harald
Sure..I rolled 6 different tubes through V1 at fire up like I always do and the amp feedback on all of them with me in the room approx 6ft from the amp..I did notice some change in sensitivity and intensity of the feedback trying different tubes.. One of the tubes I tried (Chinese Shuguang) which had a mu of 109 on the tester made the amp difficult to control in PAB (with my Hollow-body) The Amphrex in there now has a mu of around 90 and seems to be about right for my taste!!

Tony

[erwin_ve]

Does the pi in other amp have the same combination? Could you plug in the guitar in the dlator: enough juice to feed the pi of your 102 built. What exactly is that non inductive resistor in the pi, could you post a clear picture of that?
Just to make sure we dont miss a big clue.

[ElectronAvalanche]

Hi Tony,

maybe it has already been discussed:

could you try to use a different filter cap + dropping resistor for V1. I could imagine that the 20uF V1 filter cap being so close to V1 could be responsible for the tendency to feedback.

You could just desolder the B+ wire to the filter and clip in a different cap (could you check the exact capacity of the orange TVA installed?).

Cheers,

Electron