[radiorich]

Hello Guys,
I am just finishing up restoring a Delco model 987087 car radio for a 1955 Belair .
Everything works and it sounds great but I decided to take a non-working vibrator not the one from this radio since it did work install this circuit board made by Peko Rf.

Anyway my issue that I am having is when the volume all the way down you hear high pitch  tone ? 
I was wondering if I need to change or add another capacitor has anyone worked with or dealt with this Peko board and had that issue ?

Here is a link to Peko RF https://www.pekorf.com/Radio.html

Here is a couple  photos of the complete amp/powersupply

[morzh]

Rich

I don't want to immerse myself into their design and such, but here are some thoughts/clarification questions.

1. When you said "everything is working", what did you use for the power conversion (since the vibrator obviously was not working, otherwise why replace it with an SS version)?
2. Whatever the reason, have you spoken to these folks about their product and possible problems? They are the first people to talk to, they are in the know. Then we would come in, if they can't figure out what is going on.
3. What is the frequency of their converter.
4. Can that frequency possibly create that audio-range hi-pitch tone as the beating between it and some of your radio internal frequencies?

[radiorich]

Hello morzh,
First All the vibrator that was installed into this radio worked the one that I used to gut was from another radio .
I did not want to destory the working one in the radio .
Sincerely Richard
P.S. I am going to email the guy .

[Chas]

Were any buffer caps replaced and with what?

Chas

[radiorich]

Hello Chas,
I completely replaced every capacitor and replaced all the off resistors and any defective wire .
I used a panasonic brand 6800pf or .0068ufd metal film 1.6k v PP .
Part no. ECW-HA3C682H

Sincerely Richard

[MrFixr55]

Depending on the frequency of the vibrator you may have to "bridge" the electrolytics with mylar or ceramic caps, as electrolytic caps are not necessarily good at filtering out high frequency noise. A standard vibrator runs at somewhere between 100 and 200 Hz. this electronic vibrator may operate at a higher frequency.

Verify that the entire metal can of the new "vibrator" is grounded.  If the can is cut for stuffing and taped, with a paper cover added, but the 2 haves of the can are not in good electrical contact, or if the shield is not physically connected to the chassis, this may cause part of the can or the entire can to act as an antenna.

Is this noise on the bench only or in the car only?  Does the noise occur only with the solid state "vibrator" and not with a standard vibrator?  Is this a single ended or Push Pull output stage?  Push pull stages should be more forgiving of common mode (i.e. power supply) noise.  However, if the noise shows up in previous stages, that is a different story.

Consider replacing the 0Z4 with a 6X5 or 12X5 depending on the car's voltage.  (Most car companies changed to 12V in 1956.)  Other than the need for connections for the heater, I believe that the pinouts are the same.  Some radios are wired to accept either tube.  Alternately, convert to silicon diodes.  The 0Z4 is a gas discharge rectifier and can contribute its own noise.

If all is good on the bench and in the car in ACC position but noisy when the car is running then determine if the noise is from the generator, alternator or ignition system.  Frequency will vary with engine RPM.  Alternator noise is a cleaner sound than generator or spark noise.

[radiorich]

Hello Mr Fixr55 ,
Here is the information off the Peko sight about the freq.
" The default frequencies for the RVB-2 are 115 Hz and 100 Hz, the latter frequency can be activated by
bridging a solder jumper: With JP3 open (not solder-bridged) the frequency is 115Hz. With JP3 closed (solder-bridged)
the frequency is 100Hz (see fig 5). The board is shipped with the jumper JP3 open (115Hz operation) unless specified
otherwise."

Here is the photo of the Vibrator  style I used and there is the metal spring clamp that is mounted to the socket that holds it and grounds the casing but one thing is I have not tried putting all the covers on yet .

this car radio has not been installed back into the car yet Also with the mechanical vibrator I don't know if it made that noise I can try it since I still have the almost new one that came with this radio it was bought on ebay !
Don't laugh but here is a photo of my powersupply

Sincerely Richard

[MrFixr55]

Hi Rich,

Yeah, read the specs after I posted. Does it come in that can or did you package it. If the latter, Great Job!!!

Are there fingers that grab the can?

One thing to try is to measure the freq of the mechanical vibrator. Seems from the notes form PeKo that the vast majority of commercial vibrators are 115hz. if the mechanical vibrator is vastly different, then the buffer cap may have to be replaced with one of higher capacitance. Square wave notwithstanding, this should be a rather low frequency hum, similar hum to that of a radio with a full wave rectifier with bad filter caps. If much higher pitch, I am scratching my head.

[radiorich]

Hello mr Fixr55,
No it did not come mounted in the can just that little circuit board and that Photo is of the original mallory one .
I will post a photo of the one I did yes there are "Are there fingers that grab the can?"
that is what I was talking about !

Sincerely Richard

[morzh]

Is the can somehow grounded?

[Chas]

Richard,

I reviewed the Panasonic specification sheets for this type capacitor and though dV/dt is discussed, there are no such specifications applicable to this construction style (model number) capacitor.

In buffer service there is a peak pulse developed from magnetic field collapse of the power transformer. Across the capacitor this pulse and its associated transients generate enough current such that the metalizing fails in a miss-applied component, the cap does not short but looses capacity. Also, these separated islands of metalizing can reconnect/disconnect generating RF.. The best way to determine the cap is failing is to look for degradation of circuit performance and also lift one leg of the cap and take a capacitance measurement.

Recall I mentioned the metalization, nothing to do with the peak voltage the cap is designed for as it is not a film failure but a "plate" failure.

The OEM cap was likely a Foil/paper with the same 1600 volt rating. The thick foil does not separate in buffer service, the paper punctures. There are caps rated for buffer/pulse service. Their specification sheet will have the rise times published, they can be foil/plastic or a thicker metalized/plastic. I found there is a resonance to the peak pulse group in the vibrator supply and it is generally around 10mhz.

I did not look for a Panasonic pulse rated cap, I am certain it does exist, I generally use a Cornell or Illinois, not that it matters, its the specs.  Further: In some vibrator powered radios that may have push/pull outputs the desired Mf value of the buffer cap is outside of a value in production at the time as to satisfying the dV/dt criteria. So, the solution was to parallel two caps of halve the Mf value to achieve the desired capacity at the required dV/dt rating, thus distributing the effects of the pulse across two caps...

Outside of the auto radio buffer this same dV/dt issue is largely ignored in regard to output tube plate filtering. Failues/leakage in such caps the pulse, though not constant, is derived when the radio receives a burst of static. The static cuts off the plate current, the magnetic field from plate current in the primary of the transformer collapses and a high voltage pulse is created. The pulse may jump at the tube socket or far worse across layers of transformer windings. Though the transformer survives it now has acid formed from the internal arc and over time destroys the windings. Using a common metallized can also lead to this failure mode as the capacitors value will degrade to the point that it is ineffective at absorbing the pulse.

The noise issue may or not be related to the buffer cap, do be sure all metal covers are in place over the power supply and that the shielded antenna lead is long enough to be away from the radio, that, the power cables to the radio are of adequate size to minimize voltage drop from the power source.

A solid-state vibrator may or not have arc quenching components in its design. Weather those can be relied on as to adequate to suppress these pulses and the noises from such in every radio, only the manufacturer can vouch for that.

Somehow, I suspect there is a "ringing" going on, either RF or AF or a combination. I would have to be exploring the radio myself to be sure and attempt a "cure"...

One can verify the nature of the vibrator power supply by use of a 'scope of at least 100mhz bandwidth and a suitable high voltage/high frequency probe. Repetitive trace is fine. Dual channel is useful to determine how far into the chassis the noise extends but with care that the probe leads are not themselves acting as antennas.

Resolving such pulse noise issues leads to the knowledge forward avoiding the repeat on another device of similar design.

Good Luck!

Chas