Sensitivty of V1

[dartanion]

It's easy enough to pop in a resistor and take it out if there is little to no difference.

I'll be messing with this amp for a while tonight. Need to get her right before I finish my Express. Don't want to make the same mistakes again.

[Allynmey]

If you use a switch, you can go back and forth quickly and make it easier for your ears to hear and remember the difference!

[dartanion]

I hear you Allyn. It won't be hard to tell the difference at all as most tubes have been really BAD in this amp. Tubes that are perfectly good in other amps act VERY microphonic is baby. I am going to try the grid stopper first, then rewire the leads to the sockets with stranded wire as I have solid in there now. If I tap the leads now, it rings like a bell. With the presence control all the way down, it induces massive squeal. It wasn't the OT primaries being reversed either. Been there, done that.

Side note:

Do you have a Komet/Asteriod schematic to share?

[Allynmey]

Dart, move the wire coming off the wiper of the volume pot out, away from the pot body at least 1/4" you will see some of the microphonics disappear. Also don't use solid core teflon (thin jacket) wire for that one. If you run it along the chassis under the board and have it too close to the pot body, it will act as a big microphone! I use pvc (sometimes stranded) with thick jacket as an insulator.

[DerStever]

Thanks Allyn - I'm having the same issue with the L-Pool on a bunch of tubes - I found ONE old Mullard that works ok and a half beaten Telefunken at 62% life. Ill give this a try today.

[Fischerman]

FWIW, I've had problems like this in other amps and it was never the tubes. If 'just about every tube' is microphonic...it's not the tubes. Unfortunately, I've never actually 'fixed' it...well, in one amp I did fix it but that's because I gutted it and rebuilt it with new boards (it was a Fender with conductive board disease). I know this isn't much help...I guess my point is to not waste time subbing a bazillion tubes when the problem isn't the tubes.

[dartanion]

I had already replaced the wires on V1 grids with BIG shielded cable. I did a long burn in last night and played it for a few hours and things started to calm down a lot. I still think I'll be replacing the solid core wires with stranded on the socket connections as they are too rigid for this amp. Tapping on any of the leads makes a bell ring tone. This is not good. It sounds great when not set on top of a speaker cab.

[mdroberts1243]

I had already replaced the wires on V1 grids with BIG shielded cable. I did a long burn in last night and played it for a few hours and things started to calm down a lot. I still think I'll be replacing the solid core wires with stranded on the socket connections as they are too rigid for this amp. Tapping on any of the leads makes a bell ring tone. This is not good. It sounds great when not set on top of a speaker cab.

I found all my tubes microphonic in V1 on the Express I built from Ceriatone... I played with a gridstopper resistor on the second triode to help calm things down.

One thing to share... I wanted to replace the Mallory 150s with OD PS for a smoother, less brittle sound (thanks Allyn!)... but what surprised me was how microphonic the 150s are! The Orange Drop PS series really did smooth the tone and they aren't at all microphonic by comparison.

[benoit]

Hold up, I thought it was tubes that were microphonic. As I understand it, microphonic tubes pick up vibrations from the speaker or other hi spl sources in the room and amplify them audibly. I can't see how a passive component would be able to induce noise into the circuit (other then the normal noise inherent in its design) unless there was some strong magnetic field messing with it.

I could be way off here. Please enlighten me.

[skyboltone]

Hold up, I thought it was tubes that were microphonic. As I understand it, microphonic tubes pick up vibrations from the speaker or other hi spl sources in the room and amplify them audibly. I can't see how a passive component would be able to induce noise into the circuit (other then the normal noise inherent in its design) unless there was some strong magnetic field messing with it.

I could be way off here. Please enlighten me.

I don't know why, I'm not a component designer but I will attest to the fact that caps can be microphonic.

[Rick]

I don't know about caps and such being microphonic, but poor solder joints sure as heck are, I thought I had microphonic tube problems on my first amp for 2 weeks, and it was a poor rotating solder joint. I've been much more meticulous about soldering ever since, it's absolutely necessary. Even blackened tube pins can cause scratchiness, I polish them till shiny now. I use shielded audio cable for all input jacks and the volume control signal wiring. That has led to an almost complete cessation of amp bugs.

[benoit]

I don't know about caps and such being microphonic, but poor solder joints sure as heck are, I thought I had microphonic tube problems on my first amp for 2 weeks, and it was a poor rotating solder joint. I've been much more meticulous about soldering ever since, it's absolutely necessary. Even blackened tube pins can cause scratchiness, I polish them till shiny now. I use shielded audio cable for all input jacks and the volume control signal wiring. That has led to an almost complete cessation of amp bugs.

Oh, I wasn't questioning that these things can cause noise in the circuit, but rather questioning whether noise introduced in a way other that what I described (i.e. vibrations being picked up by the tubes themselves) was microphonic or something else altogether. I was under the impression that it was a fairly specific term.

[Allynmey]

Caps can be microphonic! Condenser=Capacitor...as in condenser Mic.

try tapping on a few of the caps in your amp and listen!

[dartanion]

With solid core wire, you get solid and stiff connections to the sockets, much like plumbing in a house. Rap on a pipe in the basement and you can probably feel it on many faucet handles around the house. No go outside a rap on the garden house. I doubt you feel or hear anything inside. Thus the need for me change out my solid core wiring for stranded wire.

[benoit]

I thought people (allyn in particular) often built with mostly solid core - is this not the case? Or is it just one of those things that tends to work for some and not for others? Or is it troublesome in a wreck (because of its being closer to unstable that other designs) but useful in other amps?