Delving into my cardboard storage box once more and a neat little oblong radio came out. It appeared to be in great cosmetic condition and when I removed the chassis the internals were really nicely layed out. Very compact and not a lot of room to work but oh so neat. Everything seemed smaller than the last few radios I have attrempted to get going and it looked all original with several smallish wax caps and a couple of red electros. The power cord had been cut off and what remained was totally u/s. The internal insulation had turned to powder.
First step is to try and find a schematic. The model number is RM2L and it is a H.G Palmer set. So far I have not been able to find a schematic for any H,G Palmer sets, let alone my specific model. If anyone has one I would love a copy. The only info I could find was on Radio Museum and it listed the following tube set. 6AN7,6GW8,6N8 and 6V4. In the meantime I will get on with checking the power transformer and output transformer as well as checking the tubes. Unfortunately the labels on all the tubes other than the 6V4 have disappeared so I will try and figure out which is which. I marked them all before removal so I can put them back in correct order. I did a quick resistance test on the power transformer primary and got about 150 Ohms at the mains plug inlet points I think that is OK but not sure. Next up I am planning to connect a low voltage ac power supply (18v ac) I have laying around and give it some power and do a bit of testing around the rectifier circuit before ramping it up on dim bulb. Anyway that's the plan. Feel free to advise me otherwise if I am going about things in the wrong manner. I will hold off the dim bulb for a day or two and see if I get any red flags here first.
P.S. I just ducked up to the shed and repeated my resistance test on the power transformer primary just to make sure I had the resistance value accurate before posting this. When testing the circuit including the on/off switch I found the switch was open circuit when on. So I have found something to fix right off the bat. The power transformer was 150 Ohms though when I bypassed the switch.

Primary resistance does not tell you much, apart from some continuity.
Any resistance to earth is a no no.
Being 1962 or there about, I would power it up with the dim bulb, but keep it at 60 watts or less.
If the dim bulb lights up and then goes down, all is good and it will probably work.
Replace any paper caps, if it has any.
It may also have some out of tolerance resistors, so half an hour spent checking them is required.
JJ

Thanks JJ. I will have a crack at fixing the on/off switch and then power up on dim bulb as suggested.

6GW8 is a triode pentode the two elements are obvious. 6N8 is a du diode Pentode pin 7& 8 are the diodes.

The general idea here is once its considered viable. All electrolytics as well as the paper caps should go. Beware of the Mica and Ceramic caps, they rarely fail. Any of these across coils should left well alone.

Dodgy wiring is a must for replacing.

Radio was made by KG Harris. Their own brand was Calstan.

I am embarrassed to report that I took the combined on/off switch/volume control pot out of the set. After trying to pry the lugs holding the switch to the back of the pot I worked out how to separate the switch. It was quite easy once I worked out a procedure. it separated easily by prying the plastic case gently off the back. All I was looking to do was spray some contact cleaner and clean up then refit. It was a disaster. I dropped the switch immediately after separating the two pieces. Half an hour on hands and knees later I recovered a spring and a small brass ring from the floor of the shed. The other pieces fell into my open palm when I originslly dropped it. I was confident I found all the pieces and tried to work out how it went back together. Anyway I have had no luck it's just too complicated. I cannot find any kind of exploded drawing online to help so I am resigned to buying a replacement 500K 240 volt rated switched pot as a replacement. It is so frustrating as that switch is a beautiful piece of work but I am certain that re constructing it is out of my skillset. So far finding a 240 volt rated switched pot is also proving difficult.
I will re fit the volume control, bypass the switch for now and give it some juice on dim bulb as advised. If it looks viable I will re cap and continue on.
Searching K G Harris RM2L has also come up empty as far as a schematic goes.

I am resigned to buying a replacement 500K 240 volt rated switched pot

Pots with switches on them are difficult to find these days, but Evatco in QLD appears to stock some:

https://www.evatco.com.au/500k-switched-alpha-potentiometer-long-shaft

Thanks GTC. They don't give much info on the specs of that pot. I am wondering what voltage the switch is rated at. I see they give max audio voltage 250V DC but nothing on the switch. Am I right to be concerned or is the switch on this pot OK for 240v mains AC? I really hope so as it looks perfect in every other respect. I will send them a query and maybe you or someone else on here can advise me in the meantime.
On another note I have been busy this morning re installing the old volume pot and bypassing the switch section. I put in a new mains plug and started the set up on dim bulb. Everything seemed fine. Nothing at first but then the bulb started to glow softly. There was no audio however so I started probing around with my signal tracer. Got signal in the first two tubes but nothing after. I still haven't sorted out the pinouts for each valve and without any schematic to go off I did not want to probe around aimlessly so I shut the set down and resolved to do a bit more study before proceeding any further. I came inside but suddenly thought I should have at least probed the wiper of the volume control. That would tell me the set was good up till there. So back up. Re start and OMG, this time I had audio out of the speaker. Not very strong but with an external antenna hooked up I could tune some stations. I don't know why the set worked on the second start up. Could it be a cap reformed during start one and worked a bit better the second time around? Anyway I have shut it down and will re cap it over the next few days and see what happens after that.

Hi Ray,


I have a stack of Pots and switch Pots that we are clearing out of the KCR storeroom which are totally superfluous to our needs and I am sure that in there will be a 500K pot with a switch.

KCR inherited a huge amount of component including pots, caps and resistors etc etc from someone donating them not aware that none of it was now suitable to the radio station needs as it was ALL for Valve type gear and in a station that has ZERO valve gear nothing there was ever going to be used with everything now solid state.

I have pushed it all to one side as its all packed in jars stashed in dozens of milk crates and I am reluctant to toss it all into the tip but we are running out of space and its most likely what will happen to it all.

I will check tomorrow when I go over to the studios and have a hunt through the jars of Pots and let you know if you are in luck.

No cost just pay whatever the postage will be from WA to NSW.

Thanks Kaka. that is most generous of you. I will take you up on your offer for sure. I look forward to hearing from you soon. I will make sure my email is unhidden. I think it already is but I will check in case you want to talk to me off forum. Cheers.

Full specs for the switch are right there on the page --- 250 VDC. The 0.25W refers to the carbon track in the pot.

(Audio) refers to the pot's taper. Audio means logarithmic, that is, for use as a volume control.

That pot suits your requirement perfectly. The shaft diameter may be different, but there are ways of dealing with that.

OK. Thanks GTC. I misread the specs. I thought it said 250V Dc Audio. Which I took to mean the volume control section was rated at 250VDC and there was no mention of the switch rating. Thanks for clearing that up. I have ordered one but I am now somewhat hopeful that Kakadumh will find one in his stash of parts and I will be able to replace it with a vintage component. But it is good to know the evatco pot will get me out of trouble if needed.

The VDC is likely a typo, and probably should read VAC.

Switching DC is more difficult than AC, as DC has a tendency to arc over, which is why you will see (say) a switch or relay rated at 30VDC and 240VAC.

Hi Ray,

Have found just ONE that should be OK and sent you an email the other day but no response so far.. So check your email please.

Lindsay

Hi Lindsay. That is great news. I checked my email and nothing received from you. I double checked the email address in my profile and I can confirm it is correct. I sent you an email just now. I look forward to hearing back on how to proceed. Thanks for going to the trouble of digging that part out. Cheers. Ray