CBS Volumax 4000

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boogieman
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CBS Volumax 4000

Post by boogieman » Fri Oct 16, 2009 2:49 pm

I have one here I bartered for some RF work. It works, sweeps okay, but seems to be a bit.... mushy. It doesn't seem to be holding peaks very tightly. I'll start with changing the PS caps, but unfortunately, I do not have a schematic for this box, nor have I been able to locate one online. I have found schematics for the 400 and the 4300, but not the 4000. If anyone can help me out finding one, I'd appreciate it.

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Deep Thought
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Re: CBS Volumax 4000

Post by Deep Thought » Fri Oct 16, 2009 3:35 pm

I've got a 4000 and a 4000A here plus a complete manual for the 4000A. Give me an address and I'll send you copy.
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Re: CBS Volumax 4000

Post by boogieman » Fri Oct 16, 2009 3:46 pm

It's not the "A" but I guess it would be close enough to do what I need to do. PM Sent. Thank you.
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Re: CBS Volumax 4000

Post by Deep Thought » Fri Oct 16, 2009 4:03 pm

There isn't much difference. I think the phase flipper was improved a bit but the basic design is the same.
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Re: CBS Volumax 4000

Post by boogieman » Fri Oct 16, 2009 9:19 pm

Yeah, the phase flipper on the 4000 could use a bit of improvement. I'll likely "upgrade" it if that is the case.
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Re: CBS Volumax 4000

Post by Deep Thought » Sat Oct 17, 2009 12:29 am

A copy of the 4000A manual is in the mail.
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Re: CBS Volumax 4000

Post by boogieman » Sat Oct 17, 2009 11:41 am

Thank you again, kind sir!
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Re: CBS Volumax 4000

Post by boogieman » Tue Oct 20, 2009 10:47 am

Manual was received yesterday. Thanks again.
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Re: CBS Volumax 4000

Post by boogieman » Sat Oct 31, 2009 2:50 pm

Question about this box...

It has 6 large axial electrolytics in the power supply section, all 250uF @ 50v. Someone paralleled a 500uF @ 50v cap to the leads of C3, making Ct for that stack 1250uF (assuming the 250's still are 250). What effect would it have to replace these 250uF with some larger ones, say, 4700uF? Or replace C1-C3 with a single 4700uF? I've upsized caps in single-rail supplies before and it had no detrimental effect, in fact lowered the noise floor a dB or two, but I never modified a dual-rail supply in that manner.

I'm thinking that larger capacitance values weren't as cheap as they are today, so adding smaller ones in parallel was the thing to do. Nowdays, you can get 4700uF electrolytics for pennies on the dollar compared to back then, and they're the same physical size as these 250's where they'd have been the size of soda cans back then. Seems most supplies today have at least 2200uF worth of filters in them.

Here's the PS schematic and a rough pic of the caps.

ImageImage
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Deep Thought
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Re: CBS Volumax 4000

Post by Deep Thought » Sat Oct 31, 2009 6:18 pm

Yeah, the bigger value ones were huge back then...axials at 4700 uF were the size of toilet paper tubes and would not have fit inside a 1 RU enclosure. It's not a good idea to go too far though. The inrush current can be enough to pop rectifiers that were not designed to handle it. The power supplies in the Volumax are discrete regulated designs though and not all of those caps are in parallel. The ones across the Zeners on the bases of the pass transistors should not be replaced with anything terribly different than what they are now because that can affect the regulator response time.
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Re: CBS Volumax 4000

Post by boogieman » Sat Oct 31, 2009 9:48 pm

Deep Thought wrote:Yeah, the bigger value ones were huge back then...axials at 4700 uF were the size of toilet paper tubes and would not have fit inside a 1 RU enclosure. It's not a good idea to go too far though. The inrush current can be enough to pop rectifiers that were not designed to handle it. The power supplies in the Volumax are discrete regulated designs though and not all of those caps are in parallel. The ones across the Zeners on the bases of the pass transistors should not be replaced with anything terribly different than what they are now because that can affect the regulator response time.
Yes, I figured the two that are across the zeners would have to stay the same. C2 and C3 could be replaced with a 500uF - 1000uF single cap, C1 has a resistor between it and C2, so that one probably shouldn't go much over 500uF. Low side filter could maybe go up to 500uF as well..
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Re: CBS Volumax 4000

Post by LA3A » Fri Nov 06, 2009 9:10 am

I remember back in the late 70's we talk to a company that would refurbish the Audimax/Volumax.
The company said they would replace all the audio caps with Tantalum caps for a brighter sound.
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Re: CBS Volumax 4000

Post by boogieman » Sat Nov 07, 2009 1:16 pm

I suppose that since I have the NRSC stick-ons with it, I'll pass on the tantalum upgrade. I'm having enough trouble scraping pennies to get the electrolytics right now. It's only going to be feeding a small 2-tube modulator with about 50mW output anyways. Still a winter project right now.

Another of my winter projects is to homebrew my own 2 band AM tombstone radio. I'm starting with a scruffy old Hallicrafters SX43, hacking the chassis down to just AM BCB and 1.8-5MHz circuitry. I disassembled an RCA 52" projection TV cabinet to use for the wood to build the cabinet. It will have an 18" Peavey woofer as well as a 3-way speaker in it. I'm going to build a 12 watt tube amp with EL84s and a 6080 tube to power the speakers. It will be a nice AM radio with "oomph" to spare.
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Re: CBS Volumax 4000

Post by meaty » Mon Jul 29, 2013 5:09 pm

Hi, Sorry for dredging up an old thread, but I have an old 4000 that needs a bit of work and wonder if the schematic is still around? Google hasn't helped much.

Thanks!

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Re: CBS Volumax 4000

Post by Dale H. Cook » Tue Jul 30, 2013 6:03 am

IIRC, Deep has a 4000A manual. Almost all of my Audimax/Volumax manuals are for the older 4xx series.
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