Aikido warm-up hum, resistor types, etc.

[cbutterworth]

I just can't stay away from this forum, can I?

The music that I hear from my Aikido / AKSA combo is extremely pleasing. However, I am still having a few hum issues. These can be characterized as:

1. Once the B+ has been switched-on (following 30 seconds of heating), I usually switch on my main amp - AKSA55N a solid-state class AB push-pull. When I do this, I get a very audible 60Hz hum (at least it corresponds better to a 60Hz PC generated tone than a 120Hz tone). After a few minutes, it seems to die away to barely audible. It could be that a greater ground lift resistance (currently 20 ohms) could reduce this further. It does not seem to be the AKSA because if I leave the Aikido switch-on for a few minutes, then switch on the AKSA, I do not get the louder hum. It seems that something maybe warming-up in the preamp.

2. After playing some music - maybe a CD or so, the hum seems more noticeable. This could simply be psychological, but it makes me feel pathological only joking.

I have resoldered all pads on the Aikido PCB, except for C5 which is mounted flush with the PCB, and I suppose that I should unbolt the PCB and resolder it for peace-of-mind.

The PSU filter capacitors are large 45uF motor-run caps bought from a reclamation dealer. They appear to be in decent condition (no dings, etc.). Could these be contributing to the noise, and as they warm (if they actually do) the hum level is reduced? I have 470K bleeders across these caps so that I can poke around without risking shock from them. If fully discharged, might they take a short while to fully charge and reach full capacity?

I used Vishay-Dale metal film resistors throughout. Could these generate some noise? If so, what sort of frequency would this be? I did read somewhere that carbon-comps are better for the grid stoppers.

My B+ delay uses an Amperite 30 second tube, which then switches a coil relay that simultaneously switches on B+ while removing power from the Amperite. Could the coil relay (Omron) be causing noise? If so, what kind of frequency?

My signal ground is only using a single run of cat5e. Should I use more substantial wire? I expect that I should as V = IR, so a heavier gauge cable should result in lower V?????

I feel very relieved at least that I am in the tweaking stage and can actually thoroughly enjoy listening.

Thanks,
Charlie

[kmtang]

What are the tubes you used in your Aikido amp?

Is the filament voltages are lifted to approx +80Vdc?



Johnny

[cbutterworth]

Johnny,

I am using 6SN7's throughout. To be precise, I have Sylvania 6SN7GTA and Tung-Sol 6SN7GTB, although I have also used some Magnavox tubes.

It may be that some of the hum is comming from the Sylvania tubes. I only got the Tung-sols today from an Ebay sale. I put them in the input with the Magnavox in the output. The hum-level was relatively low, even on start-up. When I put the Sylvania in the output, the hum was louder on start-up.

The heater is AC and is referenced to 1/4 B+ which is about 68V based upon 270 B+.

My Sylvania's test well - 2600 for each section (or thereabouts). The Tung-sols about 2100 for each section.

Regards,
Charlie

[tube-lover]

hi cbutterworth,Johnny & kmtang,

why not considerate 12sn7. good 6sn7 now is too expensive.

12sn7 still can use reasonable to buy excellent tubes.


tx


thomas

[tube-lover]

hi cbutterworth,

probably the circuit will had little different between your choice & mine.

During I test for the circuit. I had experience use dale resistance in the input tubes plate loading & cathode resistor & generate some noise( because of temp rise) , Pls try to use large watts dale or parallel two samll one Otherwise use Tantulum resistors.

hope this can help.

thx

thomas

[Original Burnedfingers]

Hi Charlie.

I did some tube rolling to see if I could come up with noise problems on my 6SN7/6SN7 Aikido.

I did

I have noise if I use any of my Sylvania chrome top green lettered tubes. I also have noise with Tung Sol and GE.

My Aikido is completely quiet if I use my 5692's or my nickle plated Russian equivalents or my cheep Russian tubes in the input position.

The Russian tubes I like the best are the 1578's check ebay# 250089132589 for a picture. Very nice tubes. The standard cheap 6N8S are quiet also.

This is in the input position I am talking about. I haven't tried rolling tubes in the second position yet but will do so later today.

[Original Burnedfingers]

Charlie,

Could you post your schematic and power supply?

[tube-lover]

hi burnedfingers,

I check on ebay about your advise tubes.

The Russian tubes I like the best are the 1578's check ebay# 250089132589 for a picture. Very nice tubes. The standard cheap 6N8S are quiet also.

price was quite high in russian tube. can U let me know the sound different between NOS tubes, only more silent!!!


I choose 12sn7 because NOS was quite cheap, i buy many two years before to keep stock. I love 12sn7 much more than 6sn7.


thx


thomas

[Original Burnedfingers]

Thomas,

I generally like the GE and the Chrome top Sylvania tubes because they have a great midrange and bass response. The 5692's are probably the best american tube in my opinion. The midrange is very smooth and detailed but the tubes are expensive.

The 1578's the nickle base Russian tube is every bit what the 5692's are and more. This tube seems to be even better
in the midrange and high frequency than the 5692 is. The standard Russian 6N8S is a quiet tube but nothing special. I don't feel it has the response the Sylvania or GE has.

The 1578 is a great value for the money. It can be purchased for less than 1/2 of what the 5692 brings. Personally I feel its a much better tube all around.

I choose 12sn7 because NOS was quite cheap, i buy many two years before to keep stock. I love 12sn7 much more than 6sn7

Thomas do you find the 12SN7 tube to be more quiet than the 6SN7?

[analog_sa]

Originally posted by burnedfingers

I generally like the GE and the Chrome top Sylvania tubes because they have a great midrange and bass response.

Are you able to supply some measurement data confirming the "great midrange and bass response"?