Early Wadley Barlow XCR-30 Mk2 - UK Vintage Radio Repair and Restoration Discussion Forum

John_BS · 2nd Feb 2012, 12:17 am

I was given this receiver to "trouble-shoot" by a friend. I think this example was made in 1973: in 1974 the schematic was updated to include an IC audio amp., different RF transistors (BF255's), and some minor tweaks to the RF/AF circuits. It's been really interesting to learn about the Wadley local-oscillator topology and wonder at how they got these radios working reliably on a production line!

It turned out that the main fault was the first RF transistor (BF125) which was caput. I've replaced several electrolytics where leakage might cause issues, and also a number of carbon composition resistors which had drifted more than 20% high. (NB the style shown at the top are the culprits: the type shown lower in the photo are fine). There was a dry-joint tap on one of the RF coils. When the radio was re-aligned, the 45MHz amplifier transistor (TR7) took off at UHF. Interestingly, this stage was modified post-'74 with a 10ohm resistor to ground from the base tuned-circuit. I've now added a ferrite bead on the base lead. it seems to be working now, bar a few spurious whistles on certain frequencies!

John

Andrew2 · 2nd Feb 2012, 10:22 am

Well done John - I've repaired three of these things in the past and the ingenuity of the Wadley loop system never fails to impress. Trouble is there are so many signals hurtling in various directions that the screening, filtering and decoupling have to be first-rate (a la RA17) to avoid whistles and phantom signals. In a small, low(ish) priced radio like the XCR-30 it can be a nightmare!
I recently had an SRX-30 for repair. It turned out just to be a duff diode, but everyone and his dog had had a twiddle at the various cores. I do wish they wouldn't do that. Once it was fixed and aligned it was quite decent, but it too suffered from some tuneable whistles etc.

HamishBoxer · 2nd Feb 2012, 12:03 pm

That proves Andy what I always say, alignment normally is only off if it's been got at.

David GM8JET

John_BS · 2nd Feb 2012, 12:34 pm

Quote:

but everyone and his dog had had a twiddle at the various cores

Andy:

Well, in this instance I'm probably the dog

.

In fact, I was very surprised to find that most of the tuning settings were pretty much spot-on. Even after nearly 40 years of use & abuse (it looks like it's had a spell in the garage or shed). However, the proceedure to align all the high-frequency stages by bending (stiff) air-spaced coils struck me as a bit impractical to say the least!

The RF transistors fitted to this example are metal-can (TO72) three-pin BF198 and BF199 made by STC. I've not found any reference to these devices in TO72 packages, nor to the radio every having these as OEM parts.

John

2nd Feb 2012, 12:17 am	#1
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,785	Early Wadley Barlow XCR-30 Mk2 I was given this receiver to "trouble-shoot" by a friend. I think this example was made in 1973: in 1974 the schematic was updated to include an IC audio amp., different RF transistors (BF255's), and some minor tweaks to the RF/AF circuits. It's been really interesting to learn about the Wadley local-oscillator topology and wonder at how they got these radios working reliably on a production line! It turned out that the main fault was the first RF transistor (BF125) which was caput. I've replaced several electrolytics where leakage might cause issues, and also a number of carbon composition resistors which had drifted more than 20% high. (NB the style shown at the top are the culprits: the type shown lower in the photo are fine). There was a dry-joint tap on one of the RF coils. When the radio was re-aligned, the 45MHz amplifier transistor (TR7) took off at UHF. Interestingly, this stage was modified post-'74 with a 10ohm resistor to ground from the base tuned-circuit. I've now added a ferrite bead on the base lead. it seems to be working now, bar a few spurious whistles on certain frequencies! John Attached Thumbnails

2nd Feb 2012, 10:22 am	#2
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,038	Re: Early Wadley Barlow XCR-30 Mk2 Well done John - I've repaired three of these things in the past and the ingenuity of the Wadley loop system never fails to impress. Trouble is there are so many signals hurtling in various directions that the screening, filtering and decoupling have to be first-rate (a la RA17) to avoid whistles and phantom signals. In a small, low(ish) priced radio like the XCR-30 it can be a nightmare! I recently had an SRX-30 for repair. It turned out just to be a duff diode, but everyone and his dog had had a twiddle at the various cores. I do wish they wouldn't do that. Once it was fixed and aligned it was quite decent, but it too suffered from some tuneable whistles etc. __________________ Andy G1HBE. Last edited by Andrew2; 2nd Feb 2012 at 10:38 am.

2nd Feb 2012, 12:03 pm	#3
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: Early Wadley Barlow XCR-30 Mk2 That proves Andy what I always say, alignment normally is only off if it's been got at. David GM8JET