Soviet East German Radio

[Terry]

One thing that I did notice is the German schematic doesn't use broken HT lines but they cross. In such a case I assume they connect.

No, no, no, no!!!! 

The fact that it is German isn't important - in the UK, virtually all circuits were drawn like that from the mid 60s on (so Germany might have done it earlier if this is the original drawing). Previous practice, in the UK at least, was to use saddles to show isolated crossings.

Where lines simply cross, they are not joined. If a dot is shown at the junction, it denotes that they are joined!

(Some circuits take trouble to stagger the two halves of one line so that the junction appears as two slightly staggered Tee junctions, but that is rare.)

In the circuit of your set, take a look at R21. The upper end is connected to C47 and the line crosses the line connecting switch contact 66 to R19. As there is a dot at this point, both are joined.

Now look at the line from the lower end of R21 which crosses the HT line and continues left towards C38. There is no dot here, so the two lines are not joined. It doesn't matter whether one of the lines is an HT line or not - the meaning of the presence or absence of a dot is the same.

You mention an alternative convention where isolated crossings are indicated by a break in one of the lines. This may be clearer but is rarely used.

[Nowhere-Man]

Ah, OK that's cleared. I wasn't sure because all my schematics for British radios have breaks and that's what I'm used to. It was a point last night that puzzled me because there were no broken lines. Should two lines cross over without a break to indicate circuit isolation it would confuse me.

[Nowhere-Man]

I have been trying to find about differences between the Mullard ECH81 and the Rohre ECH81. I found that the Rohre standardises with a 33 K feed to oscillator anode. Certainly in the Valve Museum cover of the valve this resistance is shown. Then I got to looking up the Mullard data in my Butterworth book. It only lists the Mullard. Of course, a few weeks ago I didn't know this distinction existed. I'm also interested in the 6U8A which is also a mixer (RCA?) Anyone know of any differences with ECH81 even with regard to audio tone?

[pwdrive]

All valves manufactured with the same type number are all more or less the same electrically, that 33k you refer to just happens to be a value selected, it could be more, it could be less, all depends on circuit design and the HT available, no difference in audio tone for different makes of ECH81, the ECH81 will work with an HT as low as 12 volts.

Rohre, so far as I know is the German word for tube.

Lawrence.

[Terry]

Rohre, so far as I know is the German word for tube.

It means valve, as I posted here: http://golbornevintageradio.co.uk/forum/...p?tid=5952&pid=64953#pid64953

Lawrence, 'tube' in English is short for Cathode Ray Tube (CRT) whereas 'tube' in American English is short for Vacuum Tube (VT) which, this side of the pond, we call a valve.

Using American terminology on a UK forum can be highly confusing, especially to members/readers with limited knowledge and should be actively discouraged. What you do behind closed doors is entirely up to you!

Of course, if you genuinely thought that 'Röhre' is the German for CRT, I apologise.

[pwdrive]

Please, don't get me going on that one, anode/plate...circuit diagram/schematic...valve/tube...should be obvious with the minimal of Googling.

Tube/CRT is also a bit sloppy...cathode ray tube is wot it is.

Lawrence.

[Murphyv310]

I have been trying to find about differences between the Mullard ECH81 and the Rohre ECH81. I found that the Rohre standardises with a 33 K feed to oscillator anode. Certainly in the Valve Museum cover of the valve this resistance is shown. Then I got to looking up the Mullard data in my Butterworth book. It only lists the Mullard. Of course, a few weeks ago I didn't know this distinction existed. I'm also interested in the 6U8A which is also a mixer (RCA?) Anyone know of any differences with ECH81 even with regard to audio tone?

Hi.
I'm sure you still have a lot to learn young man regarding how things are done. Any Pro-Electron, US and Russian valve with the same type number "should" conform to the original spec no matter who made them, Mazda, Pinnacle and others were often re-badged Mullard/Philips valves.
It's a bit like a car tyre eg a 165/13 with its V or R ratings will conform to that spec whether its a Michelin or Goodyear.

The HT feed resistors to the ECH81 are not universal but in many cases around the value you have stated.
The mixer stage has no relevance on audio tone, it can be changed by characteristics of the IF stages and the bandpass of the IF transformers and of course the audio stages themselves.

[Terry]

Any Pro-Electron, US and Russian valve with the same type number "should" conform to the original spec no matter who made them, Mazda, Pinnacle and others were often re-badged Mullard/Philips valves.

I like the emphasis on the 'should', Trevor!

I remember when the PCL85 became very difficult to get hold of - probably not long before it was replaced by the 'new and improved' PCL805.

We took this up with our Mullard rep when he called round one day. Yes, there was a world shortage of PCL85s but it was being exacerbated in the UK by the way the bulk users - such as the large rental chains - bought their valves.

They were supplied in bulk and untested, apart from a batch test - unlike individually boxed valves sold to the independent retailers which were all individually tested. In lieu of a return-under-warranty system, as the anticipated failure rate was estimated to be 5% or less, a feature of this bulk supply scheme was that the buyer could claim an additional number of valves - I think the figure was 7½% - instead. However, there was a catch to this as the buyer stipulated what type of valve comprised the additional 7½% and the manufacturer had to supply that type.

What happened, our rep explained, was that as soon as rumours started circulating of a shortage, all of these bulk users started specifying that this extra supply must be of PCL85s, no matter what type the order for the bulk was for.

Essentially, they were stock piling to the detriment of the rest of the trade who only got what was left over.

He also said that they had been offered bulk supplies of PCL85s by a foreign manufacturer but Mullard had examined them and refused to put their trademark on them. However, they thought that Mazda had snapped them up.

Sure enough, a week or so later, our back orders for the PCL85 were filled with Maxda branded valves - a very high proportion of which were subsequently return for replacement under guarantee!

[Nowhere-Man]

I found a fair few existing debates on the aforementioned valve. The issue was data differed for the German equivalent and the Valve Museum does some cover of it . Now as to whether non-native speakers like Miguel could get confused, in Cuba he has his pick of tubo or valvula. It's the same choice. The Russians also use "tube" as in trubka but the usual term is lampa. There's a third variant I can't recall.
That aside, I am curious to find where the break is around the piano keys. I never hardly work on modern circuit boards so just read up a bit on tools. Today I'll buy some useful items for desoldering. It may turn out to be a simple repair but I can clean the board too.

[Nowhere-Man]

This is a bit new to me but I'm led to believe the manufacturer is Telefunken. At any rate some guitarists were discussing subtle tone differences between RCA, Mullard and Telefunken. So I assume my ECH81 is Telefunken but a Mullard could also be employed. Three weeks ago I just referenced the valve and it came up as Mullard but then I noticed the German on the label when I pulled it. Apologies if this is a bit boring. Musicians are very touchy on valve audio characteristics. Many will have preferences.