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WB6YYS
10-27-2008, 05:50 PM
I am looking for the electronic schematic
for a PYRAMID PHASE-III Model: PS-25
Power Supply.

Any help would be greatly appreciated.

Thanks,

Beau Palmer
WB6YYS
bpalmer@surewest.net

WJ5O
10-27-2008, 07:31 PM
Beau,
I sent You an Email with a schematic for the PS-35 ....Hopefully it will be close enough to help. :)

OK, I'll post the schematic ....guess I never thought that others would need also.
http://userpages.troycable.net/~wj5o/PS-35.jpg
It just takes me a little time to get this on my ISP...... Hope others that need it will also see this post.

W4BD
10-27-2008, 08:13 PM
WJ5O

Well it sure would be nice if you could post the schematic on here. I have a Phase III Ps 25 also that ain't working.

W9GB
10-27-2008, 08:27 PM
Beau -

The Pyramid company of the Phase III era no longer focuses on the low-end CB radio / car audio market.
The Pyramid Car Audio company focuses on the car audio, guitar amp and audiophile -- larger market that spends more $$.
http://www.pyramidcaraudio.com/items.asp?category=Power+Supplies+%2F+Inverters

The Phase III design (1970s/1980s) used the LM723 IC regulator with 2N3055/2N3771 NPN pass transistors.
To learn more about linear power supplies that use the LM723, see the Repeater Builders web site (Astron web page).
http://www.repeater-builder.com/astron/astron-index.html

The Phase III design suffered from an undersized heat sink -- so I recommend adding a 80 cm computer fan (12 VDC) on these heat sinks.
The electrolytic capacitors used by Pyramid were 25 VDC units --- and overall capacitance is usually too low.
I usually select 35 VDC units and use 1,500 to 2,000 uF per AMP output.
So a 20 amp supply should have 30K to 40K uF for the DC capacitors.

w9gb

KA1MDA
10-27-2008, 11:55 PM
I had one of those Pyramid Phase 3 PS-25 power supplys in the early 80's, and used it for about 10 years. The only problem I ever had with it was the rectifier shorted one morning when I turned it on. I replaced the rectifiers with a generic ECG 40A, 800V PIV bridge. Never had a failure with it again.

One thing I noticed was the PS-25 was quite imune to RFI on VHF, but had very bad RFI at HF. Running 100 W on HF would cause the voltage regulation to go nuts. I fixed that problem by installing three .1 uF/600V capacitors on the output terminals- one from PLUG to GROUND, one from MINUS to GROUND, and one from PLUS to MINUS. Solved the HF RFI issue.

Tom, KA1MDA
www.ka1mda.org

KA9IVY
01-27-2009, 05:50 PM
I just inherited a Pyramid Phase III 35 Amp Power supply. Does anyone have a user's manul for it? It seems to work fine, but I would like to know what the buttons are supposed to do.

WJ5O
01-27-2009, 07:37 PM
Well, I have the schematic so I must have the 1 or 2 page operations manual somewhere on the premises....... I'll take a look under the bench......:o

I GOT IT...on the way to KA9IVY via QRZ listed Email

W9GB
01-27-2009, 08:19 PM
QST magazine has articles on repairing linear power supplies of the
LM723 IC regulator and 2N3055/2N3771 NPN pass transistor design ..
December 2005 QST issue
http://www.repeater-builder.com/astr...y-analysis.pdf

Repeater Builders -- under their Astron category.
You will find that the Pyramid Phase III was an attempt to produce a Far East copy
of the Astron models (most failed in quality of assembly and parts selection).
Place an Astron schematic side-by-side with the Pyramid -- The LM723 design has been fairly standard since 1970s
http://www.repeater-builder.com/astr...ron-index.html

David Metz's Classic article on linear DC power supplies
http://www.repeater-builder.com/astr...on-article.pdf

w9gb

KA9IVY
01-28-2009, 01:50 AM
Bill, Thanks so much for the manual. It is just what I needed.