New 1967 Traynor YBA-3 - Noisy Crackling When Idling

[vinylcollecter787]

I recently purchased a 1967 Traynor YBA-3. It has been modified to take 6550 power tubes. All tubes are nearly new, although there is a static/crackling sound while the amp is idling, and as notes decay. Ive heard this could have to do with resistors on the preamp tubes, or that the amp could use a cap job.

Any ideas?

[Rob Mercure]

First off you do probably need the filter and other electrolytic caps replaced if this hasn't been done. While the originals may seem to work well enough their still far beyond original design life and loss of the bias filter could be "fatal" to your output section and possible PT.

With that said your complaint is more likely due to dirty tube sockets, dirty pots, and/or dirty jacks. Cracked carbon comp resistors can produce some strange noises but you'd notice that all during the notes cycle, not only during decay.

Read R.G.'s tube amp repair FAQ and if you've got the skills clean the amp up and do a cap job - if not take it to competent tech.

Oh, and now that there is a "big bottle" 6CA7 being produced again you might consider ditching the 6550s. The 6CA7 has a "tone of it's own" much warmer than the 6550s - the 6CA7s also tend to tolerate the high screen grid voltages a tad better than the 6550s.

Rob

[vinylcollecter787]

Thanks for the advice. Im planning to take the amp in for a cap job next week. Any more information about the big bottle 6CA7's?

[Rob Mercure]

I'm not sure what you'd like to know - but these are the valves that the amp was designed for and they have, IMHO, a more "woody" or "natural" tone than the 6550s. Ask any specific and I'll try and answer.

Rob

[vinylcollecter787]

Any brand in particular? How do these differ in tone from regular EL34's?

[Rob Mercure]

The EL34 is a "soft vacuum" small plate pentode while the 6CA7 is - or at least is commonly reported to be - a "beam" pentode with a larger plate and a "harder" vacuum (funky terminology I agree - "harder" being fewer stray gas molecules). Generally the 6CA7 will sound just a bit more like a beam power tube and it reminds me somewhat of the sound of 8417s and 7591s while the EL 34 is some how "sloppier" and "brittle" - but that's what my ears provide, others probably have differing opinions. In general I really don't like pentodes as output tubes as much as BPTs but the 6550 is one of my least favorite BPTs.

Rob

[vinylcollecter787]

I thouroughly cleaned the pins of the preamp tubes and their sockets with some alcohol and noticed a big improvement. A very quiet idle, and all the way up the volume, unless im playing of course!