Philips 957 series amps...

[vk5la]

Hi All
First time poster,
I have a oldish Philips c/a 50/60's Model S957 Valve pa amp that I'm considering restoring/modifying into a small guitar amp.
On one input marked microphone it's using an EF86 and on the PU input it's using a 6N8. The 6N8 seems to be handling the tone controls as well. Unfortunately the markings have worn off the phase splitter valve but internally it looks fairly similar to a 12AX7. The output tubes are a couple of 6V6Gt's in push pull. The power supply was valve based, but the Valve is missing and someone has wired 4 diode in a bridge config for the HT voltage. The output transformer has taps for line voltages as well as a 2 Ohm (yes 2 ohm) tap as well. The amp works, I have tried it with an electric guitar in to a couple of 4 ohm speakers in parallel, and while it seems to work fine, I'd like to restore and optimise it for guitar.
Has anyone here had experience with this amp? Is what I'm proposing feasible/worthwhile? Would it be beneficial to change the power supply back to being Valve based?
Is there available somewhere a schematic? I see there is a post on the 957 amp but the pics don't show up on the page...

Cheers!
Andy

[xtian]

Cool amp, man! Welcome.

Regarding tube vs. solid state rectifier: measure and report voltage on plates (pins 3) of power tubes. If it's not too high (over 450v) I'd leave the diodes.

[darryl_h]

Possibly the best man to talk to would be Tim Robbins. Tim has restored a number of Australian-made PA amplifiers, including several Philips models.

His amplifier projects are described here: http://dalmura.com.au/projects/amplifier.php

Tim is a member of several amp-construction forums, including TAG. He generally has the forum username trobbins.

[vk5la]

Thanks for that,
I have decided to go down the path of modding it to a fender based amp and having a switchable 5Y3/solid state rectification...there seems to be an awful lot of info out there, just have to sift through it!!!

I intend to document the process here and post pics and mods etc etc...

Cheers
Andy

[vk5la]

Oh,
I forgot to add xtian, I'm seeing about 365 volts on the plates of the 6V6GT's

[Dingleberry]

Beautiful amp!
I'm in love with those old cage amps.

If you want to build a fender style amp take a look at the cj eleven.
Sort of a mix between blackface and tweed (princeton/deluxe).

That would fit perfectly to the existing control panel layout found in your philips.
And also the tube compliment is the same. 2 x 9-pin preamp tube, 2 x 6V6 and rectifier tube.
Two volumes (pre amp and master), bass and treble.
You can keep the original cool looks and aesthetics!
Easy to mod and fine tune to your needs.

Below is a schem from other forum attached just for your inspiration.
Some soundclips can be found in youtube too.

-T

[vk5la]

Thanks Dingleberry,
I've decided on the Tweed deluxe circuit, as the existing Valves and transformers will accommodate that circuit nicely. There is a Choke in the current power supply, and I'll probably leave that in, as I'm reading that its beneficial for tightning up the bottom end. I also plan on having a switchable
ss/5Y3GT rectifier. I recently obtained a NOS 5Y3GT and have a plate voltage of 326 volts. The Cathode resistor in the current circuit is 275 ohms, fairly close to the 250 ohms spec. in most circuits...This weekend I plan on fitting an IEC power socket and tidying up the 240V wiring and locating the choke to the top deck...I'll probably end up getting a cieratone or other brand turret board wired with all the components as that seems to be a time/cost effective solution for me...more later!
Andy

[vibratoking]

Great decision. The tweed deluxe is an AWESOME circuit...In my top 5 all-time as Miles has been known to say.

Best of luck and let us know how you progress.

[vk5la]

OK! progress so far...
I decided to strip the power supply section of the amp out ready for rewiring and the addition of the IEC mains socket...ended up stripping amp chassis out completely due to the fact that the soldering throughout the whole thing is an abomination, so I figured I'd rebuild it from scratch...the top cage of the amp is off to the powder coaters on Monday to be redone, in the mean time I'll have to drill a couple of extra holes for the bits I'm adding....

Valve sockets? do I renew them? (the original ones are plain bakelite, no shields...) or reuse?

This is Fun!!!

Andy