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In the sound coming from the left channel of my st70, there are noises which I can only describe as "beeping". It is not a hum or an oscillation.

When I move one or the other of left EL-34s, I can sometimes reproduce this beeping.

Is it an output tube, a socket or a poor solder connection going to a socket? Fairly recently, I did reflow the solder to every connection in the amp.

I could switch the right and left output tubes of the amp to rule out a bad tube, before "going into surgery" on the amp.

When the beeping first occurred, it ceased after the amp heated up. Now, it is does not cease to occur intermittently, despite a hot amp.

Could it be a connection going to ground temporarily or opening temporarily?

This is most likely an RF interference issue, possibly from a nearby cell or cordless phone, or wireless internet device. Most newer cell phjones use pulsed digital rather than analog FM signas, and the RF pulses can get into just about any sound system, radio, etc.

/ed B

EWBrown wrote:This is most likely an RF interference issue, possibly from a nearby cell or cordless phone, or wireless internet device. Most newer cell phjones use pulsed digital rather than analog FM signas, and the RF pulses can get into just about any sound system, radio, etc.

/ed B

I'll yank the plug on my wireless router, then report back. I am pretty sure, however, that the problem preceded the installation of the router.

Hi,

What happens when you switch the left and right input cables?
And the left and right speaker cables?
Does it continue with NFB disconnected?

What does the "beep" wave form look like?

I don't have an oscilloscope but I have connected the speaker outputs to computer's sound card inputs, used Microsoft sound recorder to record it to a WAV file, viewed the wave form on one of those free sound wave viewers that used to come bundled with sound cards.

Sometimes a wave form can tell you a lot.

You can also use the sound card to generate test signals, too.

Poor man's signal generator and oscilloscope...

Matt

MassMat wrote:Hi,

What happens when you switch the left and right input cables?
And the left and right speaker cables?

It is not a cable thing. It is an intermittent series of beeps in the left channel, with no signal (or with signals) passing.

I can reproduce the beeping by flicking the rear, left EL-34 tube, lightly.

What does the "beep" wave form look like?

I don't have an oscilloscope but I have connected the speaker outputs to computer's sound card inputs, used Microsoft sound recorder to record it to a WAV file, viewed the wave form on one of the free sound wave viewers.

Sometimes a wave form can tell you a lot.

You can also use the sound card to generate test signals, too.

Poor man's signal generator and oscilloscope...

Matt

I do not know what the waveform looks like.

Removing the wireless router did not solve the problem.

I can reproduce the beeping by flicking the rear, left EL-34 tube, lightly.

An intermittent connection at the tube socket, perhaps?

Matt

MassMat wrote:

I can reproduce the beeping by flicking the rear, left EL-34 tube, lightly.

An intermittent connection at the tube socket, perhaps?

Matt

That is what I initially thought, but flicking either of the left channel el34s reproduces the beeping. It sounds like interference problem.

If you're walking around with a NON-Verizon cell phone on
your belt ... move it away. Otherwise, the best way to
troubleshoot interference is to move the amp to another
spot, try it with inputs shorted, other equipment disconnected, etc.

Are you close to a cell tower ? Radio tower, anything like that ?

There isn't much around the house I'd suspect, just any
wireless devices.

Is it constant, or just now and then ?

... tom

TomMcNally wrote:If you're walking around with a NON-Verizon cell phone on
your belt ... move it away. Otherwise, the best way to
troubleshoot interference is to move the amp to another
spot, try it with inputs shorted, other equipment disconnected, etc.

Are you close to a cell tower ? Radio tower, anything like that ?

No. The problem just cropped up. It happens with or without a source connected to the inputs.

There isn't much around the house I'd suspect, just any
wireless devices.

Is it constant, or just now and then ?

... tom

It is sporadic and unpredictable, but I can reproduce it by flicking either of the left el34s.

kheper wrote:It is not a cable thing. It is an intermittent series of beeps in the left channel, with no signal (or with signals) passing.

I was thinking more in terms of speaker cables acting as antennas picking up the mystery RFI.
Do you have any SS devices inside your chassis such as a CCS, a power delay relay, or a CIA bug? :o Yellow_Light_Colorz_PDT_06
Or could it be something mechanically induced such as a scratchy bias pot sweeper or frayed output transformer wire insulation?

Please let us know what you find out....

Matt

perhaps you are just going insane? if you put on a tinfoil hat, does the beeping stop?
Yellow_Light_Colorz_PDT_05
i have an external ADC(an interface for recording audio into the computer) that creates bizzarre sounds in any radio, tube or transistor, that happens to be on and within 20 feet, when my computer boots up. but it is predictable and only at boot up. do you have a similar digital computer device that could be "going to sleep/waking up" during the course of your hi-fi listening sessions?
couldn't maybe bad/miswired capacitors maybe make pulsing noises that might be described as "beeps"? microphonic tubes? your pacemaker?
when i was growing up and learning how to play guitar i was plagued by somebody constantly saying through my (crummy, transistor)amplifier, for years, "please call Oscar"....i can still remember it to this day. that, and morse code pulses.

TomMcNally wrote:If you're walking around with a NON-Verizon cell phone on
your belt ... move it away. Otherwise, the best way to
troubleshoot interference is to move the amp to another
spot, try it with inputs shorted, other equipment disconnected, etc.

Are you close to a cell tower ? Radio tower, anything like that ?

There isn't much around the house I'd suspect, just any
wireless devices.

Is it constant, or just now and then ?

... tom

I am curious. What is the difference between a verizon and non-verizon cell phone?

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.

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.

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