Utility Keen Vernon MT Mid Brown BlackCascade 6SwRq4ZSxd

Utility Keen Vernon MT Mid Brown BlackCascade 6SwRq4ZSxd Utility Keen Vernon MT Mid Brown BlackCascade 6SwRq4ZSxd Utility Keen Vernon MT Mid Brown BlackCascade 6SwRq4ZSxd Utility Keen Vernon MT Mid Brown BlackCascade 6SwRq4ZSxd Utility Keen Vernon MT Mid Brown BlackCascade 6SwRq4ZSxd Utility Keen Vernon MT Mid Brown BlackCascade 6SwRq4ZSxd

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BlackCascade Keen Brown Vernon MT Mid Utility
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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Brown Utility Mid MT BlackCascade Keen Vernon
Join Date: Apr 2009
Brown Vernon MT Utility Mid BlackCascade Keen Location: Aylesbury, Buckinghamshire, UK.
Posts: 1,521
Ferrograph RTS2 restoration

Purchased this at the last Harpy' complete with matching ATU (Auxiliary Test Unit).
Spent a bit of time bringing the unit up to peak performance.
Here's a brief run down of the work carried out so far.
1). Clipping of scope output - re-biased amp by adding 82k in parallel with R174.
2). Squegging of oscillator output - replaced R7 which had gone high value.
3). Several noisy pots - carefully drilled hole in casing to allow contact cleaner to be sprayed on the track.
4). Inability to null phase control - replaced and adjusted RV121 which had gone intermittant.
5). Pickup of oscillator output at input socket - fabricated shield to reduce pickup.
6). Pickup of mains hum - re-dressed mains wiring away from pcb's.
7). Pickup of W&F 3,150 Hz tone - disconnected +30 V supply to W&F board*
8). Pickup of scope output by mV meter causing self oscillation on lowest range - connected scope output direct to pcb, by-passing W&F switch.
9). Noisy scope output - bypassed R150 with 82 pF to reduce the HF gain. Now 1dB down at 100kHz which is acceptable and has dramatically reduced the noise level. Also replaced MR31 which had gone noisy.

I've manipulated the diagram to make it easier to follow and print out, see attachments.
* I only intend to use this unit for distortion measurements, so can live without the W&F functions. The changes I've made can be easily reversed.
BTW there's an error on the meter_amp schematic, the moving contact of SW6b should go to the contact j/o R154 + R155 in the position of SW6a shown.
Brown MT Keen Mid Vernon BlackCascade Utility

BlackCascade MT Brown Utility Keen Vernon Mid
Rob.
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Last edited by glowinganode; 25th Mar 2013 at 1:05 pm.
 
25th Mar 2013, 1:52 pm   #2
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Re: Ferrograph RTS2 restoration

I remember that Wilmot Breeden owned both Ferrograph and Wayne Kerr around this period, so I've got a feeling who did the RTS2

David
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25th Mar 2013, 6:21 pm   #3
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Location: Bristol, UK.
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Re: Ferrograph RTS2 restoration

MT Utility Keen Vernon Mid BlackCascade Brown
It seems it didn't want to give in without a struggle !
Brown MT BlackCascade Keen Vernon Utility Mid
What sort of residual distortion does this read with a direct OUT / IN link ?

PS. whats "Squegging" ?

dc
 
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Join Date: Apr 2009
Utility Brown Keen MT Vernon BlackCascade Mid Location: Aylesbury, Buckinghamshire, UK.
Posts: 1,521
Re: Ferrograph RTS2 restoration

Hi Dave,
I managed to get the residual distortion down to approx 0.015 % THD @ 1 kHz.
Squegging occurred due to too much LF feedback, causing pulse modulation at around 10 Hz PRF of the output signal. It's a bit of an old fashioned term really, more applicable to RF instability in a regenerative receiver.
David, going by the age of the components, this was manufactured late '73 which I think pre-dates the Wayne-Kerr / Rendar merger. The badge on the rear states London and South-Shields, I believe Wayne Kerr were based in Bognor Regis. I do have an Audio Response Analyser which was built a few years later ('77?) which was marketed under the Ferrograph name as well as Wayne-Kerr.
See attached photo's of the holes I drilled in the Colvern wire-wound pot to allow lubrication, and the shield around the input socket (made from a bit of Quality Street tin). The trace nearest the edge of the pcb is the oscillator output which was being picked up by the input socket.
Rob.
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25th Mar 2013, 10:49 pm   #5
BlackCascade Vernon MT Brown Keen Mid Utility Dekatron
 
 
Utility Vernon Keen MT Brown Mid BlackCascade
BlackCascade Vernon Mid MT Brown Utility Keen Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 10,471
Re: Ferrograph RTS2 restoration
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Utility Mid Vernon MT Keen Brown BlackCascade
Neat work with the drill, Rob.

Yes, I think that's earlier than the merger. My W-K bridge has Ferrograph 7 knobs on it.

Squegging is where an oscillator is starved of DC power and it pulls down its supply when it runs until it stops, the supply goes higher and it restarts. Hysteresis makes it work as a relaxation oscillator.

A more complex version is 'Motorboating' in a superhet where the audio in the output amp pulls down a weak battery, the LO stops, so the sound stops, and the battery recuperates a little.... and so on.

Cheers
David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
 



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