EmRR

Re: RCA 96-A from scratch
« Reply #80 on: April 16, 2020, 03:37:35 PM »
The customer likes 4 in meters, simple as that and to be honest, that hood meter is quite ugly IMO.

No.....!   It looks amazing in person, and is the work of one of the foremost art deco designers in America!  But you're right, they are amazingly hard to find.  Custom to the Deluxe line amplifiers.   And.....the 96-AX does have the 4" meter. 

Its almost impossible to make exact copies, where would I get the transformers for example?

There was just a complete original set of 86-A transformers on ebay, FWIW.    They do show up, I've seen it several times.   But yes, if you go looking, you might not find, though you could find 'similar enough' original make units.  You have to enjoy the 'search and discover' though. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde


mjrippe

Re: RCA 96-A from scratch
« Reply #81 on: April 16, 2020, 03:52:25 PM »
The customer likes 4 in meters, simple as that and to be honest, that hood meter is quite ugly IMO.

Its almost impossible to make exact copies, where would I get the transformers for example?

What I can do is use original tubes and keep the audio circuit the same and hopefully the sound will be pretty close too.

DaveP

Unfortunately "The customer is always right".  I agree with Doug on the beauty of the deco style meter and concede the point that it was later made with the other style. 

I saw that lot of 86-B iron too and though the price was reasonable I just didn't see myself building one.

EmRR

Re: RCA 96-A from scratch
« Reply #82 on: April 16, 2020, 04:08:38 PM »
Still, looking good Dave!  Amazing amount of work to get it that close. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

EmRR

Re: RCA 96-A from scratch
« Reply #83 on: April 16, 2020, 04:30:06 PM »
Here's the best quality original picture I've found of an original installation, from the time of installation.    This has to be an actual print from the negatives RCA used for promotion.  Download the original size so you can see detail.   

Note this installation is 'transmitter gray', equally common at the time but less common now since it went into larger installs that were more likely to see forced demolition by accountants, versus small stations where things just 'disappeared' upon retirement. 

The PSU is above the amp too, which is the recommended mounting, and in fact, you can't rotate the hinged chassis out if you put the PSU on bottom as everyone now does. 

https://www.flickr.com/photos/wmar_archive/9592239562/sizes/l/
« Last Edit: April 16, 2020, 04:44:31 PM by EmRR »
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

DaveP

Re: RCA 96-A from scratch
« Reply #84 on: April 16, 2020, 04:38:46 PM »
Thanks Doug, we could almost date it by the guy's suit!

DaveP
Soundcloud: Delayed Action.

EmRR

Re: RCA 96-A from scratch
« Reply #85 on: April 16, 2020, 09:56:43 PM »
Another 'Transmitter Gray' install, this one with the PSU under, but with a spacer panel in between.   

https://www.gettyimages.com/detail/news-photo/technician-monitoring-equipment-in-studio-of-local-radio-news-photo/72400108

You can see the color here:

http://www.arizona-am.net/PHOENIX/KB7OCY/KB7OCY_op.jpg
« Last Edit: April 16, 2020, 10:03:54 PM by EmRR »
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

DaveP

Re: RCA 96-A from scratch
« Reply #86 on: April 19, 2020, 12:12:38 PM »
The main compressor circuit is now finished, but not the side-chain.  At this point I thought it wise to test the amp to see if it was OK before proceeding further.

First I ran it up to full power before clipping, this surprised me as I was not expecting much from the type 89 tubes.  It managed to put a clean 24V rms across a 600 ohm resistor, thats +30dB! or 1Watt.

Next I checked the Signal:Noise ratio and at maximum output it was  -74dB unweighted.   The original quotes -68dB so I am very pleased with that.  Considering there is no NFB in this design, this is a great credit to the RCA engineers of the 1930's.

Turning to the frequency response, I tested this at a more sensible output of +4dB.  The input level was -2dB

I ran it from 10Hz to 30kHz and despite the dip at either end, it was still within +/- 1dB from 20-20kHz and this was with off-the- shelf modern transformers.  As this compressor is designed for some old school character, it looks like it will fit the bill.



Next job is to assemble the attack and release switches and connect the side chain.

DaveP

Soundcloud: Delayed Action.

DaveP

Re: RCA 96-A from scratch
« Reply #87 on: May 02, 2020, 05:17:17 PM »
The components are all fitted now and some pics will follow soon.

These very poor pics show how I modded the meter bulb holders to accept warm white Led's.

This is the original with a 6V bulb.



The spring connector was removed and the LEDs carefully glued into 5mm dia washers, with Araldite.



Longer leads were soldered on and covered with heatshrink tubing.



Then the LED assembly was glued into the lamp holders.



These LEDs work well in series drawing about 17mA which is just under the rated current.

Sorry for the poor picture quality, too busy to redo them, but you can see how it was done.

DaveP

Soundcloud: Delayed Action.

Re: RCA 96-A from scratch
« Reply #88 on: May 11, 2020, 12:29:22 AM »
Amazing work Dave!


Would you mind sharing links to the exact handles you used for the chrome vent replicas?


DaveP

Re: RCA 96-A from scratch
« Reply #89 on: May 11, 2020, 05:35:19 AM »
Hi Alan,

The chrome bow handles came from      https://www.morehandles.co.uk/hafele-cordelia-bow-handle-107-66.html     In a pack of 16 so 8/side.

The cup handles were  from Amazon UK     Koofizo┬« Cabinet Cup Handle - Chrome Shell Shape Furniture Pull, 3 Inch/76mm Screw Spacing, 10-Pack

https://www.amazon.co.uk/gp/product/B07MQZRR5Z/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

I very carefully cut the lips off then sanded flat on a sand paper sheet.

All the best
DaveP

Soundcloud: Delayed Action.


Re: RCA 96-A from scratch
« Reply #90 on: May 11, 2020, 10:09:22 AM »
Thanks Dave!

DaveP

Re: RCA 96-A from scratch
« Reply #91 on: May 13, 2020, 01:10:55 PM »
The lettering and sealing is now done, so time for the final finished photos.



Switch far left is GR on off so you can hear the difference.  Next switch selects between GR and the Balance test, which is adjusted with the next pot.  Normal attack and release switches.   Meter switch between Tube Test, GR and Output level.  Threshold, then meter zero and compressor on/off.   At the back there is a pot to set the B+ to 250V and a pot to set the GR tubes bias to -3.9V.



Here is what's behind the front panel.



Cover on and it needed a handle.



Full point to point construction with busbar.

This project is now finished and awaiting final set-up and test before shipping.

Thanks for your interest and support

Best
DaveP

Soundcloud: Delayed Action.

IBart

Re: RCA 96-A from scratch
« Reply #92 on: May 13, 2020, 02:02:42 PM »
 :)

Incredible !!

Re: RCA 96-A from scratch
« Reply #93 on: May 13, 2020, 05:45:22 PM »
Amazing!

DaveP

Re: RCA 96-A from scratch
« Reply #94 on: May 20, 2020, 08:25:07 AM »
This is the compression I measured on minimum threshold.



Input to comp was +4dB,  non-compressed amplification line extended for reference.

DaveP
Soundcloud: Delayed Action.


 

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