First Express build, but weird harmonic

[Paultergeist]

Thanks for that additional insight, Gingertube.

In the past, I guess I have simply accepted the dogma of "the tighter the twist -- the better" with respect to heater wiring, but I never actually tested or verified this instruction. More recently, I have encountered build shots of amps with little or even no twists to heater wiring -- and these amps were obviously built by individuals who knew what they were doing -- so I knew that there was more to the story.

Your input makes sense, and it at least provides a data point which seems to have been derived by actual experimentation.

Thanks again for the reply.

[BLT]

Here's the finished product.

[Colossal]

Looks great BLT. Anything special going on with those 1x12s? Ported? What speakers are you running? Series or parallel?

[BLT]

One cab is ported with a Jensen Tornado in it. The other is a Tone Tubby ceramic and the 2 are running in parallel. They are in single cabs to save my 60 year old back.

[BLT]

The original subject for this post was about a strange harmonic I was getting with certain note combinations. I moved on to other builds and concentrated on amps that fit my style better than an Express. From the beginning I put in 6V6s to test it and never progressed beyond the 6V6s. I finally bought TAD EL34Bs and after installing and running through bias, I sat down and played a bit. After awhile I noticed the harmonic problem was gone, and nothing but nice dynamic richness of the EL34s was coming through. I've done some tube rolling prior to the new tubes, but now I have a renewed interest in trying to mitigate some of the noise. Everything else seems easy in comparison to this thing. The search continues.

[gingertube]

Don't know if anyone else has experienced the same thing as I have but my experience with maybe a dozen amp builds is that 6V6 need BIG grid stops compared to EL34/6CA7. 15K is the minimum I use for 6V6 but usually use 27K or even 33K - why? Coz I had a number of 6V6 Amps suffer ultrasonic oscillation which I traced to the power tubes. The usual 4K7 or worse 1K5 are not enough. That may account for your experience.
On the one Express I built I also found I needed 4K7 grid stops on the phase splitter triodes and I needed 22K grid stop into the last gain stage. I don't know if I needed it or not but the 2nd gain stage also got a 22K grid stop.
Cheers,
Ian

[BLT]

I have the 1K5s as you suggested. What was the dynamic you were experiencing to necessitate all the grid stoppers? My intent was always to get EL-34s, but I chose to ignore the amp for awhile and work on something else. It's obvious to me that my Express is just a better EL-34 amp than it will ever be a 6V6 amp. Having said that, my next amp will be a variation of the 6V6 Gibson GA-40.

[gingertube]

The amp just had weird distortion when pushed a bit. This was the Ultrasonic oscillation cutting in and out.
Suggest 15K minimum grid stops for any 6V6 Push Pull.
Coincidence - not long ago been asked if could do a GA40 Clone. Checked my shelf and I have everything needed in terms of trannies and tubes.
Will be very interested in your GA40 build. Want to start a thread? There is a thread I started, think here but might have been over at ampage requesting schematic details for the GA40.
In midst of a kitchen renovation so wont be starting on it soon.
Cheers,
Ian

[BLT]

Right now I'm starting to rebuild amps for a Leslie 122 and a Hammond H100. I probably should have said guitar amp.