Altec 9470A / 9475A rack-up

[emrr]

Looks right.

Here's some other 9470A connector part #s:

Amphenol 225-21022-101
Cinch 251 10 30 220
(manufacturer?) VK10D/1-1

The 9475A connector is impossible to find.  There's some telephone gear in the US that they can be robbed from, and that's about all I've found.  Same connector on the Altec 458A, 459A, and RCA BA-21A. 

 

[Whoops]

Hi,

I have 2 of these modules, and I'm starting to collect info on how to rack them.

What do you think is the best solution to adjust gain?

Using an 1K Pot or an output attenuator like the one from classic API?
http://classicapi.com/catalog/product_info.php?cPath=48&products_id=210

thanks

 

[bpucekov]

I finally managed to rack this two ALTEC 9470A preamplifier and see the wonders of one of them receives the radio station. The problem is definitely in the preamp. Anybody got an idea where to start looking

 

[emrr]

One of the (many) ground/shield connections is still not connected.  Very common mistake, so double check that.  This can also make the unit draw far too much current and damage the transistors.  I think I've already mentioned this in one of the threads here. 

 

[bpucekov]

Thanks Doug, solved, was a ground of course

 

[bpucekov]

still have problem with one 9470a module
in highest volume settings start receiving some german radio station
this time definitely not wiring problem because second module works normally with same wiring
last 5 days tries to solve this unsuccessfully
everything looks good, all voltages looks ok
any ideas
thanks in advance

 

[emrr]

I still think there's a ground issue.  Reason is these are fixed gain amps, so you should see interference related to something in the amp all the time, regardless of external volume setting.  That to me suggests something about the wiring related to whatever attenuator you are using, but you say you are swapping modules and getting ok results.  So maybe not.  Swapping other module to card edge connector? 

Check the shield and ground connections within the module also, especially the one from circuit board to case.  Remelt the joint.  External module cover on, or off?  Loosen screws that might create a ground connection, and retighten. 

 

[bpucekov]

Yes I swapping other module to the card edge connector.
I will check all ground connections one more time tomorrow.
No difference with or without cover.
Thank You for the advice.

 

 

[bpucekov]

I again checked all ground connections, no result
Replaced all transistors with those with the correct module, no result
I compared the voltages with those from the correct module, everything looks fine
Checked most of the resistors
I become desperate
Help please

 

[emrr]

Did you swap all the transistors from one module to the other?  Am I reading you correctly?

If so, did you move the ones from the bad unit to the good?  If so, what result in the formerly good?

Or did you replace the old transistors with new ones?

It sounds like they both work, just one has interference issues.  Is that true?  Can you compare gain from one to the other and see that they match in that way?

How are you changing gain?  Input or output attenuator?

 

[bpucekov]

Did you swap all the transistors from one module to the other?  Am I reading you correctly?

Yes

If so, did you move the ones from the bad unit to the good?  If so, what result in the formerly good?

Yes and good unit still works ok and bad unit is still bad

Or did you replace the old transistors with new ones?

No

It sounds like they both work, just one has interference issues.  Is that true?  Can you compare gain from one to the other and see that they match in that way?

Yes, both unit work, just one have interference issues, gain on both unit is the same


How are you changing gain?  Input or output attenuator

1 k ohm potentiometer on the output

Thanks for helping

 

[emrr]

Have you tried throwing it across the room?    ;D

A new list, to make sure I'm not missing something or interpreting incorrectly.  I am temporarily out of new ideas.  I wish I could see the situation in person.  I will try to ask too many questions here. 

module 1 works in either wiring harness.
module 2 has radio in wiring harness at full gain on output attenuator, but works ok at lower gain setting.  (barely lower?  ok at 99% pot rotation, but not 100%? does radio come on suddenly at one volume, or does it come up in volume with final part of pot travel?)

both modules deliver proper gain, and show typical current and voltage.

A complete transplant of transistors from one module to the other does not make the problem move to the other unit, nor does it solve the problem. 

connector pins 8, J, and H are all connected together a a single point somewhere, and are tied to ground.  We went through a diagnosis on page 2 of this thread, that I'm sure you have studied, but worth mentioning again. 

input connector shield is tied to case ground at the connector end, and not to module ground. 

ground connection at AC wall outlet good?  Try connecting to a different AC power source to be sure of ground?

Is it possible to take and post any pictures?

 

[bpucekov]

Have you tried throwing it across the room?    ;D

A new list, to make sure I'm not missing something or interpreting incorrectly.  I am temporarily out of new ideas.  I wish I could see the situation in person.  I will try to ask too many questions here. 

module 1 works in either wiring harness.

yes

module 2 has radio in wiring harness at full gain on output attenuator, but works ok at lower gain setting.  (barely lower?  ok at 99% pot rotation, but not 100%? does radio come on suddenly at one volume, or does it come up in volume with final part of pot travel?)

Radio come on after about 10 sec  after power on


both modules deliver proper gain, and show typical current and voltage.

yes

A complete transplant of transistors from one module to the other does not make the problem move to the other unit, nor does it solve the problem. 

correct

connector pins 8, J, and H are all connected together a a single point somewhere, and are tied to ground.  We went through a diagnosis on page 2 of this thread, that I'm sure you have studied, but worth mentioning again. 

pins 8, J and H are all connected together on card edge connector an tied to ground

input connector shield is tied to case ground at the connector end, and not to module ground. 

yes

ground connection at AC wall outlet good?  Try connecting to a different AC power source to be sure of ground?

yes                                                                  no diference

Is it possible to take and post any pictures?

 

[bpucekov]

picture 1

 

[bpucekov]

picture 2

 

[bpucekov]

picture 3

 

[bpucekov]

picture 4

sorry but do not know how to put more pictures in the same post

 

[emrr]

Running out of ideas here, without having hands on them.  Are the two electrolytic caps replaced? 

 

[bpucekov]

Running out of ideas here, without having hands on them.  Are the two electrolytic caps replaced? 

Me too.
Electrolytic caps are replaced.
Thanks to the efforts
I think I'll change the components one by one until it stops

 

[emrr]

I would re-melt every solder joint, if you haven't already.  Then start with the other film caps. 

The question is, what is acting as a radio antenna?