This post is just an observation Guys.

I’m finding its getting hard to source here in Aus. old stock of 7 pin miniature phenolic valve sockets with a centre tube as they were originally made.

Ceramic 7 pin types are everywhere on the Internet, and not hard to source but I’m not real keen on these, so I’m going to give this type a miss.

If any of you Guys have a few of these original 7 pin miniature phenolic types in your kit of parts , hold on to them close, as they are getting scarce and pricey.

all the best Guys

Interesting note on Wafer Type Valve Sockets

To re- read the construction notes regarding the build of the 1956 Little General from Radio TV and Hobbies was interesting, especially concerning the use of wafer type valve sockets , something I didn’t do.

Philip Watson in his build article of June 1956 of the Little General noted the use of 7 pin miniature valve sockets of the Wafer Type.

He went on to say, quote “ Wafer Sockets, Valve sockets are available in a number of designs but we have
deliberately chosen wafer types for this set. In one position at least (the 6BH5 ) this type has certain
electrical advantages and we have used it in other positions for the sake of uniformity” he goes on to say, “

We suggest that the moulded type be avoided in this set, particularly for the 9 pin miniature 6BH5 (I.F.) since there appears to be a greater tendency to instability with this type, apparently due to greater capacitance between pins”

I haven’t been able to ascertain if the 6BH5 itself was unstable under certain conditions or higher frequencies, but it appears in this case to be set off by stray capacitance in phenolic sockets.

I must have glossed over that part of the text, and the use of the phenolic type in my case went without issue.

There are two positions that get seriously hot, Rectifiers & PA. If I have to replace a socket there I prefer ceramic. An annoyance I see with those two tubes in a HMV I haven't bothered to identify, before attacking it, is the proximity of the 6M5 & 6V4; To the power transformer.

Not only does that risk induced hum, its not doing the outer wrapping of the transformer a lot of good. Perhaps one with "Bells would have been better?. Big solder blobs in close proximity are never helpful. Fluctuations in supply voltages can upset oscillator, & pentagrid tubes

Marc

I would imagine ceramic sockets would always be preferable for so many reasons.

Instability is usually related to layout, bypassing etc.

Brins, an interesting observation about sockets.

The Bakelite sockets 20's to 60's were a product of the technology of the time using punching methods along with tag strips and rotary switches. Cheapness in bulk.
The one supplier could do all those parts as a subcontractor and make purchasing life a bit easier.
Yes mouldings were expensive in Bakelite, punched Bakelite a lot cheaper.
"Plastic" mouldings became available in the 50's but the Bakelite's had a big advantage in production.
You could solder on the assembly lines using irons that were big and hot as hell ( by todays standards) and not fry punched Bakelite where plastics just melted! Note what happens when you go near a polyplasticy coil former like an IFT with a big hot iron, the pin sinks into the moulding, eeeeeeeeeeeK!

From a technical point, there may be a subtle capacitance thing, but I have used Bakelite, moulded Bakelite, moulded plastic and ceramics in scratch built equipment where I have had to develop designs from audio work through to FM frequency.
I used ceramics for hot or high frequency work if I could, and that was really the criteria for selection, a practical selection not a pre-conceived techo selection.

For some hot and high voltage use like a 300watt+ stage amp (700 volt plate supply) or a EHT convertor, ceramic bases were a must, for the heat and thousands of spike volts buzzing around. I arced over Bakelite sockets in those uses (ah the smell of burning Bakelite!) and never did it again.

I note that once into the 10's to 100's of mega cycle all normal bets are off as the inductance and capacitance of normal sockets with wiggly connectors that act like coils and leaky insulation (at that frequency!) becomes significant. That was probably what Phil was referring to. Not of any consequence in an AM band radio, but at UHF, hell yes!

Freddo.

If I have to replace a socket there I prefer ceramic.

Ditto.

Thankyou so much Guys its so interesting to go back over this.

We can all agree, ceramics are the best with stray capacitance and voltage breakdown .

My dramas started many years ago when I was put off using Ceramic’s with miniatures valves because of a couple of disasters I’d had with breakage in hot swapping.

6BH5

1951 Philips release Notes…….. Only released in Australia

Philips Quote, “In the design of the 6BH5 which is intended for RF and IF stages of standard A.M. receivers due account has been taken of accepted commercial standards for associated components used in Australian receivers and its electrical characteristics have been chosen accordingly.
The mutual conductance of 2200 umhos with a cut off bias of -39 volts, a grid to plate inter-electrode capacitance of 0.002 / uμF maximum and a plate resistance of 1.0megohm will be found to give stable results without imposing difficulties in regard to the choice of
associated components.
The 6BH5 include special internal shielding to provide low inter-electrode capacitances and obviate the need for an external shield can.”

It is possible that the 6BH5 had design limitations and had issues with higher frequencies, and may have been limited to A.M. receivers