Korting (German) console chassis

[Motorola minion]

A customer who bought the EMUD I had restored, seems to like these so much they got a Korting console, yanked out the chassis and brought to me and asked if I could give it a go after a stereo shop condemned it as unfixable - BALONEY.

Seems that a few wafer-thin tube sockets need replacing. The pins were not in a circle, but a square pattern, so I drilled bigger holes in PCB to accommodate new molded black tube sockets. The 12AX7 shields are soldered, so you need to remove them to get tubes out. Odd construction but good build quality like the EMUD.

This uses a pair of 12AX7s but an unusual output tube for each channel; 6HU8/ELL80 which is a pair of beam power pentodes, connected in push-pull configuration, using rather small output transformers. One of the output tubes was weak, fortunately the Fisher Ambassador I had scrapped use them.

Several types of caps are used in this chassis. The pink wax-paper ones were failing yet none of the gold ones tested bad, I replaced all the paper caps on the amp PCB. The electrolytics tested ok as well I can only assume the problem was the tube sockets and a frozen bass control which I loosened up. The buttons work, radio works.

[William]

I never understood German radios. My aunt and uncle had a Telefunken table radio that worked and sounded great, and I have no idea what happened to it. I had a Grundig console radio, no phono, given to me that was a piece of junk. When I picked it up to load it in the truck the cabinet literally fell apart. I loaded it anyway and brought it home only to find the circuit boards and PT fried. I pulled the tubes and speakers, and the rest went to the landfill the next time I went. Does anyone know the pecking order on quality for German radios/phono's?

Bill

[Hi-Fi-Mogul]

Nice work there !

The customer should be pleased.

How are the black tube sockets secured to the PCB ?

I like the perforated tube shields idea they had.

[electra225]

I had a Saba 300 that was one of the best radios I ever heard. When it worked, which was seldom. Name a part in that thing and it gave trouble at some point. Like Bill mentioned, the cabinet, made of mystery pressed board, was horrible. If a dog peed on a fire plug two blocks away, the cabinet would swell and start coming apart. Elmer's construction glue was all that held it together. I sold it at the auction. No more German radios for me.

[Motorola minion]

Once upon a time, I stopped in a downtown Lancaster thrift/pawn shop "Chris's Buy and Sell" that was clearing out after its owner decided to retire. The only things of interest left were a 1930's floor model radio, pair of Cerwin Vega speakers in good condition and a Korting 931 with obvious varmint damage. I am assuming what looked like water damage was due to an extended stay in a city building with all kinds of mishaps and "visitors" over the years.

I salvaged just the tubes, chassis, glass and record changer. The pushbuttons all worked yet the switch contact board was peed on as well. Only the legs and lift lid were worth saving, speakers were trashed, grill cloth stained several shades of who knows what. The usual EF89/EABC80(6T8)/ECC85/12AX7 tubes included 2 good 6GW8 that I used to repair a Japanese-made tube receiver that was riddled with bad resistors and paper caps. It sounded just OK.

The point of referencing the other parts chassis is because I used both its single-ended 6GW8 single-ended OPT's to replace the right channel P-P OPT. Once I get the polarity right, determine if I parallel or place secondary windings in series, I will post a schematic.

The biggest issue finding a replacement push-pull OPT for a 6HU8, is matching the unusually high winding impedances. I have already tried a P-P 50C5 opt, p-p 6F6/6k6 universal replacement with poor volume and tone. These lower impedance transformers do not allow the 6HU8 to operate within its design parameters.

These Euro-styled consoles are cute and sound sweet when set up right but...I DEFINETLY prefer USA made stuff!

[Motorola minion]

The 6HU8 / ELL80 was not listed in the Hammond transformer catalog, but the attached transformer has enough windings to optimize for this tube. There is only one data sheet at POCnet, few others made this tube, which was intended also used in televisions as a horizontal (line) oscillator.

The one I ordered from Ebay was the 125D at $42. No decent output transformer is less $ anyway.

The windings are listed on the BV1214 at left, the failed original. The two OPTs from 6GW8s on right.

[TC Chris]

How does one identify a German console lacking a nameplate? Somebody gave me a mono console long ago, missing its record changer and speaker.. I subbed in an old 6x9 and it played happily. It's been sitting in the back room since I moved in 1995.

They all looked the same in that era--glass slide-rule dial; concentric knobs at each end; pushbuttons under the dial scale and a little edgewise knob at each end. Kinda like modern cars: all the same.

Chris Campbell

[Motorola minion]

The build methods change but the control arrangements rarely do, with countries and cites noted on SW bands. The parts and sometimes even tubes that were used differed and gave few clues to the manufacturer.

50s-60s German tube sets' identification is sometimes on the glass, more likely speaker or front trim with model name also, BUT always found on the dark brown back covers, where the only tube map can be found

The now-rare 6GW8 and others began as cheaper, more modern alternatives to combine functions in same envelope but also doomed it to high-failure as it was used in lots of TV circuits and table radios as well.

The manufacturers below I assume had most market share due to favorable pricing,
making their importers a s**t-ton of $$. And as any HW Sams Photofact Scholar will tell you, model listings are sparse and sometimes issued in a set number, often a few years later as a "bulletin or SED file"

Nordmende-Sterling imported those, etc
Majestic imported Grundig
Delmonico imported Korting, others.
EMUD - Leowe-Opta - etc

SABA is probably the best of them all, a German make comparable to Zenith

[Motorola minion]

The Hammond 125D came from Mouser, though I bought it on Ebay. Only had selection of the 10 watt unit, yet its oversized and has numerous secondary speaker taps, presumably to match load of variety of tubes.

The 125D's primary was a single, center tapped so I measured the primary DC resistance (190+190 ohms) and conclude it will NOT work. Not wasting my time tacking it in, it will sound just like the other transformer I had (PP universal 6F6/6K6/41/42) This transformer will probably be used to fix a Motorola using 6V6 or 6BQ5.

After looking online at a few manufacturers including Hammond, I can conclude there is no replacement that will match the extremely high DC resistance of 1500 ohms is needed. 5300 turns of .08mm wire, at one ohm per foot, that's 1500 feet of 40 AWG!

I will make one more post, showing how I put the two SE 6GW8 transformers in series to couple the ELL80's plates to the speaker.

[maxidyne]

I've been following your posts, but have not had any comments about the project that would add to the discussion. Would it be possible to change the output tubes to 6BQ5 or another type that you could get an output transformer for?

[Motorola minion]

I've been following your posts, but have not had any comments about the project that would add to the discussion. Would it be possible to change the output tubes to 6BQ5 or another type that you could get an output transformer for?

That would be an option if I had those transformers, left channel works fine, so I can't really justify putting even bigger units in with limited room. Anything else I do I probably can't add to the bill for this customer, If I can get decent sound from the other channel. Their main concern was crumbling tube sockets after the one 6HU8 melted down.

In case of output tube meltdown, the cathode resistor is overloaded-yes, but the OPT gets the worst of this overcurrent condition. In this case, one-off designs to use tubes that were more available, so a custom-wound audio output transformer was needed.

I am posting this mainly as a cautionary tale. I have a super clean Telefunken Hymnus 5216 sitting next to my Pontiac in a remote garage. Once powered up it let out some magic smoke, I was told. Two of four 6GW8s tested as if burned down like candles. After 6 years, there is no desire to dig into it, especially after this experience!

[TC Chris]

I am posting this mainly as a cautionary tale. I have a super clean Telefunken Hymnus 5216 sitting next to my Pontiac in a remote garage. Once powered up it let out some magic smoke, I was told. Two of four 6GW8s tested as if burned down like candles. After 6 years, there is no desire to dig into it, especially after this experience!

I was luckier. I found a Sansui 1000A receiver at curbside with brand-new 7591 RCA output tubes (and other tubes new too). But.... One channel's 7591s had melted. The Sansui used oil caps that did not, it is said, last long. Somebody had amp problems, replaced tubes, and the new ones melted too. So they put it at curbside. I replaced all the caps and scrounged some used 7591s. The OPT and power trans. survived.

One source said this receiver was Sansui's effort to equal or better the current Fisher and Scott receivers and it is generally admired.

Chris Campbell