On My Bench.

[Dave the bass]

Oui.

[Dave the bass]

A while back our-Nigelspinner got in contact regarding a chum who had an identical Pye P75 radio to the one JTS and I had got from our-Ed while we were on hols up in Louth.

Nigel (very) kindly collected the P75 and a bonus Barker 88 and so when we were on a hols down his neck of the woods last year we arranged to meet up and collect the wooden lovelinesses. Ta again Nigel, much appreciated!

Picture taken before I started a major tidy up process of the bench, P75 on bottom, Barker 88 on top.


The chassis comes out like this to make it easier to work on which is handy as I'm new to this.


This radio works OK on LW and MW but is silent on SW which is OK with us (for now) as we only use it to listen to Caroline on 648kHz on MW. It just needed switches and pots cleaning thankfully as it had undergone a light restoration a few years back by Nigel's chum I believe, it sounds superb when fed with the long wire antenna I've got strung down the garden but downstairs we use it on its own internal antenna. Maybe I'll go deeper into the SW fault if it needs a service or attention in the future and I've learned enough to understand how AM radios work and what to look for!

It now lives in harmony with a Pair of Falcon LS3/5a I built a few years ago and a pair of Quad ESL57 that need attention but are too big to get through the loft hatch for storage, ooooppss!

Vintage audio corner...


The Barker 88 needed a 5Y3GT rectifier and the internal speaker had been disconnected too for some reason. This one hadn't been used in a longtime but had been worked on before as a few caps have been replaced by the looks of it. The connectors on the thin paxolin(?)/bakelite(?) board that fits directly onto the loudspeaker were in poor shape so I've fitted modern connectors here and reconnected the internal speaker...


It was filthy with dust and cobwebs, a web-covered volume pot!...


I like the little 'service hatch' you can remove to work on it!..


After a clean up, new rectifier and speaker work its another working radio, whahey!


The non-essential-but-oh-so-cool (IMO) 'tuning indicator' doesn't work on it though unfortunately, its a 6U5G.


... the top of which pokes through this hole in the fascia of the radio here...


Other than that, its a go-er but needs an external antenna feed as there's no internal fitted on this one, meh. Its got a very meaty sound to it, its got 2 x 6V6 in PP as the output stage and the speaker itself is quite large but fragile and 'dry looking', but it works.

Whahey!


I've still got our-Ed's P75 to do, that was low sensitivity on all bands IIRC that Ed warned us about, I'll have a look at that when I've ran out of current projects. Approx. mid-2042 I reckon.

Onwards.

[Mike H]

Phwoar! Jealous!

[Mike H]

The non-essential-but-oh-so-cool (IMO) 'tuning indicator' doesn't work on it though unfortunately, its a 6U5G.

Quite a few 6U5G on eBay at the moment, if it's actually the valve that's faulty.

[Dave the bass]

Next project, a 1985 small handheld Airband radio, a mate found it in a WEEE bin at his workplace whilst electro-wombling and thought of me. He's kind, I'm a sucka

Dead, wont power up, fault found a fuse soldered to a pair of wires (!) blown due to short across the supply rail. Found a 22uF 15v Tantlum cap in the RF section gone short. Removed it, unit now powers up. Whahey!

Question, Is there any reason not to replace a Tantlum with a same value electrolytic? Thankfully physical space isn't a problem for such a small value cap in this case.

[simon]

Dunno Dave, but the only place I've used tants is in 3 leg regs and I think the data sheet recommends much higher values of electrolytic than tantalum?

Not much help.

[andrew Ivimey]

I remember when tantalum bead caps were new brightest kids on the block ( spect you do too really) - they were very small. But Ud use anything that claimed the right mfd and were safely within voltage. Once up 'n runnin again I'd worry about aesthetics.

Could be wrong though!

[Mike H]

Only times I've seen tant's used is for small size. They're not good for audio anyway. So yeah do it.

[pre65]

Dave, I found a couple of what I think are tant caps in the number 14 capacitor spares box.

They are marked,

0 u 22 +
40 VR +
25VC M
S5
PHILIPS

Radial leads.

Any good ? I can post.

[Dave the bass]

Ta for your thoughts all, I was wondering if there were any specific characteristics that Tantlum caps had that electrolytic don't, or vice versa.

Ta for the offer Phil but I think your caps are 0.22uF if I'm reading that correctly.

The transceiver works without that cap but obviously it's there for a reason. Maybe it's part of the transmitter circuitry, I've no info on it as it's a mid 80s American radio that appears to have been used in light aircraft to contact control towers for landing permission and approaches I'm guessing and what I've found on the net.

I'm hearing planes approaching London City on it, so it works as a receiver very well. The battery pack is missing so I have to use a bench PSU.

Good fun though getting it to power up.

[Mike H]

Google 'tantalum capacitor vs electrolytic'

Quite interesting. Apparently tants can be more prone to failure. ESR and leakage can be good, but may be non-linear over a frequency range.

[Dave the bass]

Quite interesting. Apparently tants can be more prone to failure. ESR and leakage can be good, but may be non-linear over a frequency range.

Aaah, now that I didn't know. Ta Mike.

Here's a few pics of it. Its a 'Narco HT 830' made by Narco Avionics.



Erks...







Faulty cap photo'd through a magnifying glass...

[simon]

Strewth! I wouldn't know where to start with that. It's almost SMD size!

[andrew Ivimey]

SMD was waiting in the wings.

[Max N]

Narco Avionics - sounds like a Colombian import-export company…