Pam 601 A & B. - UK Vintage Radio Repair and Restoration Discussion Forum

andrew65 · 22nd Feb 2019, 6:48 pm

Hi all.

I'm new to here so not sure how it all goes. I have a question for you all I have a Pam 601A and 601B. What is the difference between the two? Also I would like to refurbish them and do they make good hifi amplifiers? Is it also true that they give out 25 watts is the per channel or combined? can they also be turned into mono blocks?

Regards, Andrew.

PJL · 24th Feb 2019, 11:26 pm

Hi, and welcome to the forum. Do you have any experience repairing valve equipment?

I believe these amps were designed for PA use and have 100V outputs so you would either need to find matching transformers or replace the output transformers.

Nuvistor · 25th Feb 2019, 12:38 am

Sales brochures at this location, yes the use 100v line out for the speakers, see reference list.

http://www.pamphonic.co.uk/html/1945-1955.html

Herald1360 · 25th Feb 2019, 10:52 am

Sounds like the 601B is not a very close match for the A, though whether you would actually hear the difference is another matter. Output power is the same at 25W.

To turn them into monoblocks (presumably by this you mean single channel "hifi" power amplifiers) you would need to lose the front end preamplifier circuits and tone controls and replace the output transformers with low impedance output ones, or add yet another stepdown transformer with extra added distortion etc to each output.

I don't think it's worth butchering a couple of nice PA amps to do that though you may of course do what you like with your own property. Why not sell them for what they're worth as they are and put the money towards what you really want?

andrew65 · 25th Feb 2019, 10:22 pm

Thanks for all the replies so far, so do you think its worth refurbishing them as they seem a bit tatty but I like the look of them.

Pamphonica · 17th Mar 2019, 9:24 pm

A quick comment on these amps.
Remember that they were designed for PA use. That means that the LF response will be far worse than a proper HiFi amp. Apart from anything else, it saves the manufacturer cost on the output transformer.
So I would not recommend these for HiFi unless I had replaced (sacrilege!!) the output transformers with well-rated 4/8/15 ohm ones to match.
That means that, once you have modified the circuits suitably, you really only have the mains transformer left from the original amp and not much else apart from the metalwork!
Do note also that the original designs used EL37s. These are NOT the same as KT66s, having almost twice the gm, so again, KT66 substitution may need a few changes to achieve apropriate overall gain.
I hope this helps a bit.
-Jeremy

22nd Feb 2019, 6:48 pm	#1
andrew65 Retired Dormant Member Join Date: Feb 2019 Location: Eltham, London, UK. Posts: 2	Pam 601 A & B. Hi all. I'm new to here so not sure how it all goes. I have a question for you all I have a Pam 601A and 601B. What is the difference between the two? Also I would like to refurbish them and do they make good hifi amplifiers? Is it also true that they give out 25 watts is the per channel or combined? can they also be turned into mono blocks? Regards, Andrew.

24th Feb 2019, 11:26 pm	#2
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Pam 601 A & B. Hi, and welcome to the forum. Do you have any experience repairing valve equipment? I believe these amps were designed for PA use and have 100V outputs so you would either need to find matching transformers or replace the output transformers.

25th Feb 2019, 12:38 am	#3
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Pam 601 A & B. Sales brochures at this location, yes the use 100v line out for the speakers, see reference list. http://www.pamphonic.co.uk/html/1945-1955.html __________________ Frank

25th Feb 2019, 10:52 am	#4
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Pam 601 A & B. Sounds like the 601B is not a very close match for the A, though whether you would actually hear the difference is another matter. Output power is the same at 25W. To turn them into monoblocks (presumably by this you mean single channel "hifi" power amplifiers) you would need to lose the front end preamplifier circuits and tone controls and replace the output transformers with low impedance output ones, or add yet another stepdown transformer with extra added distortion etc to each output. I don't think it's worth butchering a couple of nice PA amps to do that though you may of course do what you like with your own property. Why not sell them for what they're worth as they are and put the money towards what you really want? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

25th Feb 2019, 10:22 pm	#5
andrew65 Retired Dormant Member Join Date: Feb 2019 Location: Eltham, London, UK. Posts: 2	Re: Pam 601 A & B. Thanks for all the replies so far, so do you think its worth refurbishing them as they seem a bit tatty but I like the look of them.

17th Mar 2019, 9:24 pm	#6
Pamphonica Nonode Join Date: Mar 2008 Location: Virginia Water, Surrey, UK. Posts: 2,877	Re: Pam 601 A & B. A quick comment on these amps. Remember that they were designed for PA use. That means that the LF response will be far worse than a proper HiFi amp. Apart from anything else, it saves the manufacturer cost on the output transformer. So I would not recommend these for HiFi unless I had replaced (sacrilege!!) the output transformers with well-rated 4/8/15 ohm ones to match. That means that, once you have modified the circuits suitably, you really only have the mains transformer left from the original amp and not much else apart from the metalwork! Do note also that the original designs used EL37s. These are NOT the same as KT66s, having almost twice the gm, so again, KT66 substitution may need a few changes to achieve apropriate overall gain. I hope this helps a bit. -Jeremy __________________ Jeremy, G8MLK, BVWTVM Friend, VMARS, BVWS Secretary. www.pamphonic.co.uk www.bttt.org.uk