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TomMcNally wrote:I don't have a technical answer - I just know that the
Verizon phones (they use CDMA) don't emit all of the
RF that interferes with computer speakers, audio systems
and so forth like AT&T and other phones do. With an
AT&T phone, you can hear data coming from various
audio devices if you sit it nearby.

Well after doing a little reading, I see Sprint and verizon use CDMA, whereas AT&T and T-Mobile use GSM. With a lot of phones going 3G, will this problem get worse or better?

EWBrown wrote:Did you check the driver tubes? Perhaps one of them is acting up.
Try swapping the channels (7199 if the original circuit, 12AX7 / 12AU7 / 12AT7 if one of the newer replacement upgrade boards.TYpically, the center tube is the VA, and the "outer" tubes are the LTPIs.

I'll get to that next.

THis still sounds line an RF situation to me...The Motorola NEXTEL I used to have was a serious RFI generator, frequency was not the standard cell band, but on the SMRS band. The newer ones use 1900 MHz (approx) PCS.

/ed B

My guess is that the problem is either interference or bad contacts in 2 sockets. Last night at least, the beeping became less frequent over time. I had the amp on for about 12 hours.

We had trouble with the cordless phones coming over the stereos with that type of noise in Radio Shack. We had to switch to analog for the store phones Yellow_Light_Colorz_PDT_09

Good luck!

Changing the driver tubes from 5693 to 12au7 has decreased the beeping, but I can still reproduce the beeps by moving the left channel output tubes.

Do you hear the beeps if you simply cup your hand around
the tube, not actually touching it ? Like an antenna ?

If not, you may have a loose socket pin, if the problems stays
with the tube when you swap it to the other channel, the
tube itself may be bad, or have a loose pin that needs to
be resoldered. Tube pins do come loose, the best way to
solder them is while they are vertical, as the solder will wick up,
then use a razor knife to clean any excess solder off.

TomMcNally wrote:Do you hear the beeps if you simply cup your hand around
the tube, not actually touching it ? Like an antenna ?

No. I need to physically move the tubes.

If not, you may have a loose socket pin, if the problems stays
with the tube when you swap it to the other channel, the
tube itself may be bad, or have a loose pin that needs to
be resoldered. Tube pins do come loose, the best way to
solder them is while they are vertical, as the solder will wick up,
then use a razor knife to clean any excess solder off.

I played the amp last night; It was a regular beep-athon.

I suspect the two bad left channel sockets.

The sockets can be tightened ... take a small jewelers
type screwdriver and bend all of the contacts whichever
way would tighten them up. For safety, make sure the
amp is unplugged, and with an alligator clip lead grounded
to the chassis, insert the other end (using and INSULATED tool)
ground each pin before you tighten them.

Also, look at the pins on the tubes, and if any of the solder
connections at the end of the pins look bad, and you can wiggle
the wire going from the pin up into the glass, hit them with
a soldering iron and make them tight and shiny.

TomMcNally wrote:The sockets can be tightened ... take a small jewelers
type screwdriver and bend all of the contacts whichever
way would tighten them up. For safety, make sure the
amp is unplugged, and with an alligator clip lead grounded
to the chassis, insert the other end (using and INSULATED tool)
ground each pin before you tighten them.

Also, look at the pins on the tubes, and if any of the solder
connections at the end of the pins look bad, and you can wiggle
the wire going from the pin up into the glass, hit them with
a soldering iron and make them tight and shiny.

I re-tensioned the socket pins. The beeping did decrease somewhat, but it remains.

It turned out to be a tube. It would not bias correctly.

When I turned the amp on, I saw a voltage for this tube, but as it warmed up, no voltage was detectable.

I have a quad of Tung-Sol KT66s, which I was saving for another project. I think I'll give them a whirl in the st70. The bias supply will be rebuilt with new caps and lower value resistors to obtain the voltage which kt66s like.

The tubes in right channel developed the same sort of beeping as the left, but they did so more noisily than the left channel did.

The right channel tubes would not hold a bias. Even plugging a probe into the pins of the sockets to take bias readings sent the tubes into beeping mode.

The tubes which failed were JJ EL-34L tubes.

I had an old, worn quad of what look to be Mullards, with no stenciling left on them. They may be 40 over years old. However, these tubes hold a solid bias and do not beep.

The JJs did not last. They were 2 years old. I did play them every day for about 3 hours, but underbiased and at low volume levels.

Forget everything I said.

The right channel tubes went into beeping mode last night. I noticed that one was not glowing and was cool to the touch.

It is either caused by bad socket contacts, bad filament (or other) wiring to the sockets.

Have you given a thought to exorcism?

Matt

J/J has had some QA "issues" recently... My most recent J/J tubes are from 2-3 years ago, so I have been lucky to miss the current crop of "dodgy" ones.

/ed B

i was soldering around a bit on my valve jr PCB this weekend, i changed out a few resistor/cap values to increase gain and alter tone. anyway, lo and behold i have heard a few intermittant beeps myself now. also some crackling frying sounds.
i lowered the value of the preamp grid resistor from 68k to 10k, which i understand is there to help block RFI...
i haven't used the amp but it almost seemed like it coincided with the furnace blower, maybe a voltage spike can somehow sound like a quick high pitched sine wave?
anyway i'm not worried about it yet, just playing around

MassMatt wrote:Have you given a thought to exorcism?

Matt

Do you mean for me or the amp?