Grundig 110a GB radio

[Mark Hennessy]

That's good news!

I agree that most of their transistor sets aren't easy to work on, but they are relatively reliable on the whole. Interesting about the tone control, which isn't showing up on the service data I have here so perhaps that's a later addition? I still haven't had a chance to unearth mine from the attic,, but will check for the presence of the tone switch when I eventually get around to it.

They did a similar thing on the Yacht Boy, only it was a bass cut switch on the tone control itself - so rotate for treble, and pull to reduce the bass. By all accounts many folk missed that.

Cheers,

Mark

[boater sam]

On the Grundig service sheet for 1998 the description is in the top right corner above the circuit for the output stage, the switch is shown connected to C55.

[Mike Watterson]

Great job Sam.

Though many transistor sets were as repairable as valve sets. Valve portables died out about 1958 and mains models maybe another 5 years, so about 20 years for the all-dry valve portables and less than 45 years for valves. The first transistor radio was 1954, so portable transistor radios longer than all-dry valve portables. I'm not sure when the last radio with discrete transistors was made, but 1999-2000 would have been the 45 year mark. Kits of AM portable using discrete transistors, that look based on 1960s Germanium designs, but with Silicon are still sold. I've had plenty of valve sets with ghastly drive cords (Philips!) and some sets (AM/FM PCB AC/DC) defeated me. There are also valve sets with unobtainable audio transformers (especially mains-battery with primary for a battery and mains pentode). The USA had all-dry portables with octal about 1937-1938, UK 1939, but the B7G all-dry from 1941 in USA. A couple of those in UK (Romac etc) after the war, but rare till 1948. The USA never had valve portable FM like continental Europe when DC90 released (those are not easy repairs, later DF97) and UK only had two when transistors already in AM portables.

Some makers are worse to work on than others. The Grundig mains tape-recorders are a lot harder to work on than the common multiple UK models of same era using a BSR deck (about 2x as many valves too!).

IC based radios (earlier ones also had transistors) are from 1967 (Sony ICR-100, and they may have had the second portable transistor set), so that's 57 years!

I have repaired some Tesco "World band" AM/FM sets. The early ones are based on a superhet IC with 10.7 MHz and 455 kHz ceramic filters and typical polycon tuner. A later version looks identical with a similar PCB. Except the polycon cap is a polymer pot and the IC has a small watch type crystal. It's using an ASIC DSP IC and doesn't work as well on LW & MW (birdies), but fine on HF & VHF. The non-IC surface mount parts are easier to remove and replace than PTH parts with a magnifying lamp. Back in 1985 when we were introducing SMT where I worked we learnt that you cut off the IC with a craft knife, clean pads and reflow new IC with a regular 3mm wedge tip iron. BGA parts need special gear.

The issue, even in 1980s, was getting replacement parts of any in-house or custom IC*, or figuring out the value of an exploded part without a schematic. Last year I repaired a Watson frequency meter (mostly SMT) where the input was blown. I traced the ground, signal and supply paths and simply soldered in a 4 pin 5 GHz transistor that seemed to match ground pads, input and output and the collector chip resistor with one for that supply volts. Input cap with a likely value and it's working now. Regular 3mm tip, desolder braid, sharp knife and tweezers from a cheap Primark set.

I first encountered SMT transistors, ICs and caps on 1" x 2" (approx) Alumina substrates that had printed resistors (trimmed by abrasive tool rather than laser then). Due to "heat-sink" nature of the substrate they were very hard to rework. That was on work experience in about 1974. Earlier some Soviet military gear used such Thick Film circuits with SMT caps and printed resistors with Rod pentodes.

You can buy hotplates, heatguns, etc for BGA and other tricky repairs cheaply. People are repairin computer, PS and Xbox mobos at home.

[* When function is obvious and speed not too high, custom ICs have been replaced by PIC micros on a a board. The original PIC was about 1976]

[Mark Hennessy]

On the Grundig service sheet for 1998  the description is in the top right corner above the circuit for the output stage, the switch is shown connected to C55.

Ah - the tone switch was added for the "a" model! Both the schematics I had here were for the non-a version.

It's strange that C155 is absent from the earlier version and no other capacitor took its designation. If you didn't know which way around the models were released, that could lead you to think that the tone control was subsequently dropped, rather than having been added. Perhaps it was in the prototype, dropped for production, then added back in for the a model? Who knows...

R41 is also added.

Looking more closely, the switch that chooses between radio and external input is mounted on the potentiometer (presumably pull to operate?) on the earlier model (if I'm translating correctly), whereas it is on the rear panel next to the DIN socket for the a model, freeing up the potentiometer switch for the tone control function.