"Old " Hi-Fi

[joebog1]

In following on from a few other members posts about older hi-fi equipment, I have pulled out an origional transformer set ( a very high quality set ) for an ultra linear 6BQ5/EL84 output stage. Its from my favorite magazine of all time, Radio, Television and Hobbies.
The actual circuitry isnt new, mostly being a revamped version of the Mullard design, right down to the preamp using 4 off EF86/Z729 in a preamp. I have all the origional metalwork and front panel for the preamp, but I chucked the power amp metalwork many years ago.

I do remember that these amps had exceptionally good performance when coupled to the right speakers. In keeping with this forum I will rebuild the origional preamp, in its origional gold hammertone box and even the tardy looking bakelite knobs with the enevitable gold line painted onto the outer ring.
I bought the power amp, and the preamp together about 35 years ago and just kept
"the good bits ". A new project is on the boil ( as if I dont have enough going already !! ) and it will be posted as I go.
A few pics of the before type. I have all the origional printed matter if anybody wants a copy.
PLease check my wanted add.


Joe

[qualityten]

Looking forward to future posts on this.

[joebog1]

So, being the type I am, I will preceed this discussion with some history. R,TV,&H always called their audio stuff " Playmaster ". Even after they changed names to Electronic Australia in 1965, they continued with Playmaster being their brand.
I have mentioned before, that to even get an interview with that journal, you had to be a qualified engineer. There was "never " any bodgy-dodgy designs presented. Their audio stuff was upmarket for the time, rivalling anything Britain produced, or at least equal of.
This preamp is essentially an Australian version of Mullards design. It was modified to suit local components in most cases, but in some instances considerable improvents were made as they would go back and "update " older designs. So here is some background.
As will be noticed, this design is for mono ( stereo was only being talked about ), but if you double up the audio circuitry, you will get a very nice stereo version. The version I will be rebuilding/refurbishing is stereo, and is from May 1960.

Joe

[joebog1]

last paragraph. I suppose I should edit these pages, but some of the adds are excellent reading in themselves. If the mods decide to advise me on that, I can cut and paste them to suit.

Joe

[joebog1]

It became obvious after stereo was well into its early years, new high compliance cartridges just wouldnt drive an amplifier to full output, without the gain control at max, so they updated the design. Here is the first update.
The reason I send all this guff is to show how they were always looking for the best that could be obtained at a normal mans wage. I suppose in one respect it was the beginning of audiophoolery, but those who bother to read these articles, they will understand why. This article was published in
June 1959.

Joe

[joebog1]

And then there six, pages again.
Newer cartridges again had lower outputs and readers wanted yet more gain. The discussion gets down to 10 mV for some carts. Imagine what would have happened if we had moving coil cartridges back then, ( Yes I know we did have ) so another update with improved balance control and yet more gain was developed.
Mainly a few resistor changes, but a major overhaul of physical layout.
This is the unit I have and will be working on. If anybody has questions or suggestions as I go, please let me know.


Joe

[joebog1]

last page.

Joe

[Uncle Bulgaria]

Colour me interested too, Joe! I'm gradually repainting all my machine tools gold. Adds a certain glamour to things.

I've collated the pages of the 1956 article and run text recognition on it so it's a bit easier to read. I'll do the rest tomorrow.

[retailer]

I've also been planning a number of valve stereo amps for a while now - I should have well and truly started one of my builds by now but other things and people with problems seem to just crop up out of nowhere - the RTV&H twin 10 is high on the list as a choice to build - I'll keep an eye on this thread and follow your progress.

[joebog1]

I have all of RTV&H from 1939 to 1965. If you say please I can copy and EMAIL ( hint hint so I dont get whacked by the perfessers from cambridge agian ) any article you wish.
Retailer, I have an "updated " version of the twin ten, entitled " a versatile 2X10W stereo amplifier.
Has lots of silly things like tape head and third speaker facilities. Also uses different voltage amp/phase splitter (7199's ). Its still a "basic " copy of the Mullard design though. After all, a wheel is a wheel is a wheel. I have always thought that to improve the wheel, an equilateral triangular item would be better. its 3 minutes: https://www.youtube.com/watch?v=zi4YQlzOYiY
Thanks for the interest guys.

Watch this space.

Joe

[joebog1]

Why do you need text recognition uncle ?. Is there anything I can do at this end to help?.
I have lots of time on my hands, so it doesnt cost me anything.

Joe

[Robert Gribnau]

Hello Joe,

Not too long ago the RTV&H issues from 1939 to 1965 were all on the Worldradiohistory site but at some point were removed because of a copyright claim.

https://worldradiohistory.com/Radio_and_Hobbies.htm

[joebog1]

Correct Robert. I have a DVD worth of them that can still be purchased, but as I am only discussing the ideas, I am not breaking copyright.
They ( WorldRadioHistrory ) also had lots of Electronics Australia, but that is owned by somebody else so they had to remove that completely.

Joe

[joebog1]

I should mention, I have probably 200 isues in very aged paper. !!!

j.b.

[Uncle Bulgaria]

Originally Posted by joebog1

Why do you need text recognition uncle ?. Is there anything I can do at this end to help?.
I have lots of time on my hands, so it doesnt cost me anything.

Joe

No particular reason, Joe - thanks for the kind offer though. I just find it handy with PDFs that are text-heavy as it makes it very easy to Ctrl-F a particular phrase when trying to pinpoint a remembrance and searching through files. I guess most people have Acrobat Reader which doesn't offer OCR text recognition as a tool, so I do it as a matter of course when processing in Acrobat Professional.

I've collated your previous uploads. I agree with you - it looks like a marvellous magazine!

Is this going to have anything to do with your Golden Ear Laboratory build?

[Ed_Dinning]

Hi Joe, one of the problems with these preamps is the number of selector switches needed all ganged to the same shaft. Is there a ready supply of them over there?

I have a good assortment if any are needed

Ed

[joebog1]

I have access to many "Oak " switches as they were called here ED. I can check and see as I still have access to thousands of them, but if they are the same pattern I dont know.
The man selling his valves would have at least a hudredweight of them in various patterns.
The one in the unit I have is in excellent condition and just needs a clean.
I have bought modern ceramic Chinese ones at VERY reasonable prices that are superb quality and very easily available. I will be using them in my valve tester.
I find a much larger problem today is the ganged pots. In my unit they are Australian made and still function perfectly, alas, like everything else we were good at, no longer made or available new.
I have yet to find Asian equivelents without speding stupid money on gold flashed superconducter already dipped in nitrogen superpots.

Joe

[joebog1]

Uncle Bulgaria, No this has nothing to do with the Goldenears, which is progressing slowely.
The thread was started as there are a few threads lately about various versions of Mullard circuits, and its my belief that one can never have too much information and discussion about ( say ) an amplifier.
This discussion group has some of finest ( aged in oak ) engineers still around from the golden age of analogue. So I actually presented it to add to the information already to hand.
With suggestions and critique from some of the brains trust here, we should end up with something resembling a Ferrari, but with ride comfort like a Rolls Royce. Best of all worlds.

Qualityten and retailer especially have shown an interest, as you have yourself.
If it does nothing more than expand your horizons, and stimulate some thinking its a good idea and not a waste of time. After all, we are a dying race as the kids of today plugin to MP3 and lo-fi garbage, I try and discuss as much as I can, with as many as I can, to educate myself, and especially if its a topic which this forum is made up of.

Does that make sense ??.

Joe

[joebog1]

For Ed, and for anyone else thats interested. Some pics of what was on top of my junk.
THese are the ceramic Chinese switches I have been buying.
The largest one is 8 pole 5 position switches. Cost about $12.00 Au so around seven quid in UK.
The smallest is two position two pole, cost about $9.00 Au, so about five quid UK.
The closeups are to show what I consider superb quality, and I have used many thousands over the years.

Joe

[joebog1]

oops!!
I have not seen them with long shafts, but I think we all have a bit of 1/4" shaft that could be coupled up if needed.

j.b.