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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
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8th Oct 2006, 9:29 pm | #1 |
Tetrode
Join Date: Apr 2006
Location: Larne, Northern Ireland, UK.
Posts: 64
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Valve screening can tip
I needed to change the screening cans on My Ferranti 145 due to rust, and had got off Ebay four cracking good ones, albeit HRO. so they did not fit snugly. I hit upon the idea of using a single plier type paper punch to make 3 dents or impressions around the bottom, so they fitted more neatly on the skirt of the valveholder... being a bit ham-fisted I managed to cut right through! No matter, it left the flap joined at the top due to the leading edge effect of the punch, is adjustable, and it worked a treat!
John, BVWS Member. |
10th Oct 2006, 9:19 pm | #2 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
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Re: Valve screening can tip
On the topic of valve screening cans, it is worthy of note that in the mid-sixties some research was carried out which established that if the plain ali screening can - as fitted to B7G & B9A valves - was painted matt black, and a good thermal contact was made with the valve envelope, the valve ran a lot cooler - as much as 20 deg. C !
Obviously, this measure substantially prolongs the valve's life. Also of note is that fact that the Racal RA-17 receiver has all of its screening cans black anodised. This is a receiver designed for continuous duty in all climates / environments, with reliability a major design feature. Al / G8DLH |
17th Oct 2007, 9:50 pm | #3 |
Octode
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,873
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Re: Valve screening can tip
During the restoration of a Bush VHF 61, I hit upon the idea of substituting a black screening can for the plain aluminium one fitted to the ECC85. The valve runs appreciably cooler which will prolong its life - ECC85s are not the best in this respect.
An added bonus was less oscillator drift. Although the Bush sets are pretty good in this respect, the improvement in tuning stability at the HF end of the band was worthwhile - achieved with not a lot of effort. Leon. |
18th Oct 2007, 12:15 am | #4 | |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,959
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Re: Valve screening can tip
Quote:
Paul |
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18th Oct 2007, 12:21 am | #5 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
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Re: Valve screening can tip
Leon -
I have an Eddystone 888A that has a ECC85 in a cascode arrangement for the RF amplifier (this is a modification). It too has a black ali can fitted - and I haven't had to change that valve for a very long time! Al / Skywave. |
18th Oct 2007, 9:20 am | #6 |
Octode
Join Date: Nov 2003
Location: Bath, Somerset, UK.
Posts: 1,805
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Re: Valve screening can tip
Back in the mid '70s, I acquired an old telefusion line amplifier. This contained maybe seven B9a valves. Each one was fitted with sprung steel black cans which had six cooling fins radiating from the circumference. Where this equipment was designed to run 24/7 this must have been essential.
Neil
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