20-05-2012, 03:55 PM
This last year or two, due to space limitations, I've tended to go for smaller sets, so at the NVCF I bought a little Noble four valve TRF, which uses an identical Bakelite cabinet and a similar dial to the Portadyne Princess. The valve line up and chassis layouts differ slighlty, in that the Princess uses two B7G and two Octal valves (Two 12BA6, 35L6GT, 35Z4), whereas the Noble uses four octal valves. (12K7, 12J7, 35L6 and 35Z4). Both sets use a twin section dropper which looks underpowered for the job in hand, and consequently are burnt out in both sets. I've started restoring the Princess and have replaced the burnt out dropper with two 50Watt metal clad resistors which should be well up to the task, for which I've made a heavy gauge aluminium heat sink as metal clad resistors can't cope with their full rated dissipation without being mounted on a heat sink. I'll need to do likewise for the Noble. The original dropper sections were 550R and 260R, so I've used the nearest modern values which are 270R (+3.8%) and 560R,(+1.8%%) which will be fine as they're well within tolerance.
Both sets use a 50k antilog track pot which serves both as the volume control and reaction control, which I've mentioned before in respect of the Princess. This could be a pitfall for unwary restorers who - if the control needed replacing - would probably use a normal log track pot out of ignorance. I've no idea whether a log pot would work satisfactorily, but I somehow doubt it. (I have managed to obtain an unswitched 50k antilog pot with a view to using the track as a donor to fit in a switched pot of a different value by changing the tracks over, but as it's only 16mm diam, I'm not sure that switched pots as small as that exist - I haven't had a look around as yet. For now, it isn't a problem as having dismantled the pot and cleaned the switch contacts with Servisol, the switch and pot work for now.
Neither set has a back, so I'll be making one with my router jig as I have a picture of what the Princess back looks like, together with the printed notice, and I've made a quick cardboard template of the shape, which fits the Noble as well as the Princess.
I've done the usual trawl of internet, R&TV books, Paul Stennings Service Data DVD and haven't fished anything up. I've attached a few pics of the Noble in its unrestored state, and a couple of the Princess part restored, showing the beneath chassis view and heatsink. Has anyone got any info about the Noble please? No worries if not - it's never been out of its case so the phantom fiddler hasn't crawled all over it, unlike the Princess, so I'll just replace the few caps, and do all the usual cleaning and fettling up tasks such as replacing dodgy wiring, cleaning and testing the valves, switch contacts etc.
Interesting little sets, though I'm not expecting them to be outstanding performers when restored. The Noble still has its 15ft throw-out aerial attached, and the remnants of its single insulated mains flex.
Both sets use a 50k antilog track pot which serves both as the volume control and reaction control, which I've mentioned before in respect of the Princess. This could be a pitfall for unwary restorers who - if the control needed replacing - would probably use a normal log track pot out of ignorance. I've no idea whether a log pot would work satisfactorily, but I somehow doubt it. (I have managed to obtain an unswitched 50k antilog pot with a view to using the track as a donor to fit in a switched pot of a different value by changing the tracks over, but as it's only 16mm diam, I'm not sure that switched pots as small as that exist - I haven't had a look around as yet. For now, it isn't a problem as having dismantled the pot and cleaned the switch contacts with Servisol, the switch and pot work for now.
Neither set has a back, so I'll be making one with my router jig as I have a picture of what the Princess back looks like, together with the printed notice, and I've made a quick cardboard template of the shape, which fits the Noble as well as the Princess.
I've done the usual trawl of internet, R&TV books, Paul Stennings Service Data DVD and haven't fished anything up. I've attached a few pics of the Noble in its unrestored state, and a couple of the Princess part restored, showing the beneath chassis view and heatsink. Has anyone got any info about the Noble please? No worries if not - it's never been out of its case so the phantom fiddler hasn't crawled all over it, unlike the Princess, so I'll just replace the few caps, and do all the usual cleaning and fettling up tasks such as replacing dodgy wiring, cleaning and testing the valves, switch contacts etc.
Interesting little sets, though I'm not expecting them to be outstanding performers when restored. The Noble still has its 15ft throw-out aerial attached, and the remnants of its single insulated mains flex.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
