View Full Version : Need PYRAMID PS-25 Schematic
10-27-2008, 05:50 PM
I am looking for the electronic schematic
for a PYRAMID PHASE-III Model: PS-25
Any help would be greatly appreciated.
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.
It just takes me a little time to get this on my ISP...... Hope others that need it will also see this post.
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.
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 $$.
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).
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.
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.
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.
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
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
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
David Metz's Classic article on linear DC power supplies
01-28-2009, 01:50 AM
Bill, Thanks so much for the manual. It is just what I needed.