Perplexed

[ToneBone]

Hi everyone,
Last year I put together the two-stroke kit from TAN. initially it seemed to work ok.. I never had occasion to turn it up much past 6 on the volume.
I decided to try some different NOS tubes and started experimenting this spring with different levels.

I noticed that when I get up to level 8 and above on the volume the amp turns decidedly “unmusical” regardless of the tube combinations I use.

ive tried a JJ 5y3
a Sylvania nos 5y3
an RCA nos 5y3

An NOS tung-sol 5881
a JJ EL-34
a JJ 6l6
a jj 6v6

JJ 12ax7
amperex bugle boy
RCA 12ax7

I can hear the different qualities of the tubes at 6 vol and below
but the distortion gets “off key” and seriously unmusical when I crank it.

I did notice that my wall current was coming into the house at 124v so I swapped the PT tap from the 120v to the 125v and it helped a tiny bit
but still when I crank the amp the sound is unusuable… it gets so bad that if I move a barre chord up a full step it sounds the same.. just horrible distorted non musical sound without a change in pitch lol.

Have no idea what could cause this.

[Robin]

It’s probably not the tubes (those NOS 5Y3 tubes are nice!) or the wall voltage. The Two Stoke should sound great running flat out. My guess is parasitic oscillation. Does the quality of the undesirable tone change when you change the “boost” switch setting? Try pushing the leads (wiring) around a bit with a chop stick and see if you can affect any change. Sometime even a very small change in the lead dress will cure the problem. Also, confirm that your grounds are good and solid, some times a weak solder joint will cause a problem. Start there and see what happens.

Please send the NOS tung-sol 5881 and NOS rectifier tubes to me at once so I can do extensive testing and confirm it’s not the tubes, I should be able to complete the tests in a couple of years… thanks in advance.

[ToneBone]

I will probe it with a chopstick lol

sorry the tubes are use in my wife’s new valve powered tea warmer.

xD

[ToneBone]

Of course I came home tonight and the amp sounded fine. So it seems to be intermittent.. so I walked away from it for awhile with it powered up.. came back to it ,cranked it .. sounded great. shut it down, had dinner.. powered it back up and the noise returned, so I probed for an hour or so with a chopstick.. every solder joint.. the amp didnt make a peep.. so I decided to pluck one string at a time at full volume.. and the bottom end.. on the E and A string I could here a loud sizzle that would come and go as the note rang out.. Definetely did not sound like vibration.. was def and electronic noise of some sort. Im wondering if I have a bad resistor someplace.

Cheers and thanks again for your comments

[Paul]

Sure it’s not the speaker? that doesn’t sound much different that what I was dealing with.

I just finished a warranty repair on the Weber speaker I put in my two stroke, because it was sounding strange and buzzy at high volumes, in particular on an open A string. took me a while to notice it because I hadnt cranked it much initially, and the buzzing was not uniform on all strings.

I had other speakers around to confirm that I had a dud…and after the repair all is well.

[Robin]

Check the 100k resistors for sure. Paul’s thought on the speaker is good too, check to see that the speaker frame is torqued evenly to the baffle board, it does not take much to induce “cone cry” when the speaker frame is tweeked. Especially in speakers that don’t have much of an air gap (like most Webers). You said you checked all the solder joints, but a weak joint can do that intermittently for sure.

I had a problem like that with one of my amps once, I replaced the speaker, changed the tubes, removed the chassis, speaker and other cabinet hardware in search of the vibration. After several hours of hunting, I finally found that one of the screws holding the component board to the chassis was causing a sympathetic harmonic at certain frequencies. The screw was tight, but a quarter turn was all it took to resolve the harmonic and the amp has worked fine since then.

BTW, the tea warmer sounds interesting, I’ve not seen one before. I can see why the NOS 5Y3 would be superior to a new manufacture tube. The new manufacture rectifier tubes are just not the same.

[ToneBone]

I have tried about 6 different speakers but thanks

[ToneBone]

Thanks, I tried all of the obvious things like above. I took some voltage readings on the output tube. The book says 340 to 360 vdc on pin 3. im getting 385 vdc. I tried a different rectifier tube ( a new jj 5y3s) Getting the same readings. still getting the horrible distortion above six.
I will keep working on it as I have time. Thanks for the input.

[Robin]

I get higher voltages than that with the solid state rectifier. The higher voltage should actually give you more head-room (cleaner). The NOS rectifier tubes should measure about 35-45 volts lower and give a “browner” tone. The Two Stroke breaks up (by design), if you are looking for a clean, chimey tone, the Two Stroke wont get it.

TAN member Mitch was having a intermittent crackling/hissing issue that sounded like a tube, even with different tubes. It turned out to be the V2 socket, pin 8 sleeve needed to be tensioned a hair and the problem was solved. Maybe there is a batch of marginal tube sockets going around.

[ToneBone]

That’s interesting that you say the nos tube should be about 50 volts less. My sylvania 5y3 is within 5 volts of the JJ 5y3. I def don’t have cone cry or anything like that. I’ve tried C10R, C10q, vintage C10N, a weber 10, and an Eminence blue frame Alnico (which sounds the best) like I said the the amp sounds absolutely fine up until 6 or so on the volume then after that it gets a horrible non musical sound that is heavily distorted and does not correspond to anything that any genre of music would consider musical. I will try the resistors you mentioned because I can’t find anything obvious that is wrong. unless I have a bad OT. idk.

[Robin]

The resistors would cause a crackling so if it’s an overtone or distortion, it’s probably not a bad resistor. Interesting that the NOS rectifier tube(s) you have are that close to a new one. I have a number of NOS 5Y3s, RCA and Sylvania mostly, and they all measure around 40 volts (give or take) lower than a new JJ or Sovtek.

If it sounds like a sub-harmonic (unnatural harmonic like a ghost tone over the note), it could be a filter cap issue, it’s unlikely with new caps, but it’s a common fix for old amps with that issue to replace the coupling caps. The OT is probably ok, but the location might be an issue if there is phantom coupling with another component. Moving it around a little bit would prove it. Also, keeping the grid resistor as close to the socket as possible and shorting wires to the grid helps sometimes. I’ve never seen these issues in a Two Stroke before but everyone’s build is a little different.

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