Valve amplifier issues... Help Please

[Fretking18]

Originally Posted by TonyDuell

From the photos it looks like it was originally a mono valve amplifier that has been 'modified' to stereo by adding a second channel -- using transistors (!).

Thanks for the advice Tony much appreciated..i can see now that the second added section used transistors rather than valves to make it stereo

[Diabolical Artificer]

Regards working with high voltage or HT, it's a case of being careful and taking a few precaution's. Somebody suggested putting your (left) hand in your pocket which is good advice. Your trying to avoid a shock across your heart across the arms, from one hand touching an earthed chassis say, to the other touching a live/HT point. So you attach the black lead of your DMM/AVO to ground and use the right hand for probing, taking reading's (heart left side mostly) left hand out the way, in your pocket, picking your nose or in your lughole.

If your a bit unsure connect any meter probes before switching on, then step back out the way. Some folk I know put a big red Warning High Voltage sign near their bench to remind themselves, it's easy to become less than 100% attentive.. Also don't work on this stuff when your tired or distracted, you have to be switched on. If you find yourself making dopey mistakes, switch off and come back later.

A.

[Ted Kendall]

Strewth, whattabodge!

Where kit has been intelligently modified, like the HMV 1804 Fernseh is grappling with, I'm all for restoration as-is. This one...I'd say ditch all that transistor nonsense and rebuild it as it was designed.

[Fretking18]

Originally Posted by Diabolical Artificer

Regards working with high voltage or HT, it's a case of being careful and taking a few precaution's. Somebody suggested putting your (left) hand in your pocket which is good advice. Your trying to avoid a shock across your heart across the arms, from one hand touching an earthed chassis say, to the other touching a live/HT point. So you attach the black lead of your DMM/AVO to ground and use the right hand for probing, taking reading's (heart left side mostly) left hand out the way, in your pocket, picking your nose or in your lughole.

If your a bit unsure connect any meter probes before switching on, then step back out the way. Some folk I know put a big red Warning High Voltage sign near their bench to remind themselves, it's easy to become less than 100% attentive.. Also don't work on this stuff when your tired or distracted, you have to be switched on. If you find yourself making dopey mistakes, switch off and come back later.

Thank you very Much for this advice ..this is precisely what i needed to know..exactly how to take precautions against Electric shocks

[Fretking18]

Originally Posted by TonyDuell

And given that it has been modified, I think the only way to know how to use the extra inputs, etc is to start tracing out the circuit.

HI Tony
Thanks for your overview of the situation..i will trace the circuits..that sounds the best thing to do
regards
Stuart

[Fretking18]

Originally Posted by Ted Kendall

Strewth, whattabodge!

Where kit has been intelligently modified, like the HMV 1804 Fernseh is grappling with, I'm all for restoration as-is. This one...I'd say ditch all that transistor nonsense and rebuild it as it was designed.

I personally do not have the skill to do that..... and from my point of view if it works in Stereo im happy,...the cartridge is wired for stereo and actually..it may not be ideal but who ever did it certainly didn't do a bodge job..i thinks it quite neatly done just not period correct.

[JacKam_]

Stuart, there is always a chance to get an electric shock, but with time you will develop that reflex...

Always wear shoes, you may also install sensitive RCD.

Good luck,

Jacek

[Fretking18]

Thank you Jacek...I appreciate the good advice

[kevinaston1]

Fretking is a trade name from John Hornby Skewes & Co. Ltd, used on guitars and effects pedals.


Kevin

[AC/HL]

Originally Posted by JacKam_

Stuart, there is always a chance to get an electric shock, but with time you will develop that reflex...

For most shocks, yes we do, but best you follow the advice given earlier.

[Edward Huggins]

Does it now work in Stereo? Did you test it with a 2nd Channel speaker?
Bear in mind that as the added amp is not orignal, and if the 2nd speaker does not closely match, the sound will be compromsed. If if were mine, I would bridge the cartridge to Mono and by-pass that dubious transistor addition. Then you will at last be able to hear it as it was meant to be heard.

[ColinTheAmpMan1]

Originally Posted by Fretking18

I don't have an isolation transformer and I can't afford to get it looked at by a valve specialist as that kind of expertise doesn't come cheap. I will just have to make sure I'm well earthed at all times. However I have no plans for modifications at all I will simply give it a bit of a clean up and put it back in the carriage once I've tested that it all works as it should.

There are a few points here:

1) I think the suggestion is that if you aren't experienced with high voltages, which can not only hurt, but can kill, then cost shouldn't come in to the question. Find a friend who knows what s/he is doing and let then have a look at your amp for the cost of a beer or two.

2) I don't think that "making sure I'm well earthed at all times" is a good idea. If you are earthed and a part of you touches a high-voltage point, you will know about it. If you are not earthed (i.e. wearing rubber-soled shoes), then your body floats to that high voltage and little or no current will flow - little or no shock. I think this belief of yours in that being at earth potential means safety indicates your lack of experience of high voltage circuitry.

3) Pretty much everyone who has commented so far has said that this is a hodge-podge and not a modification by Dynatron. It will never be good stereo due to the complete mismatch of the valve- and transistor-amplifiers. It just may give the impression of two channels, but "works as it should" is pretty meaningless, really. Having said that, my first "stereo" experiments were with mismatched amplifiers and speakers, but boy, did I want a proper stereo set-up, even if cheap!

Sorry to sound so damning, but I wouldn't like to find out that you had given yourself a serious electric shock over this mess.

Colin.

[Fretking18]

Fair play Colin and thank you for the great advice..my use of the word "Earthed" was incorrect but my meaning was that,i know to wear rubber soled shoes,I will heed the advice given in the previous comments in regards to how to treat this high Voltage device with the respect it needs in order to stay safe

[kalee20]

Originally Posted by TonyDuell

From the photos it looks like it was originally a mono valve amplifier that has been 'modified' to stereo by adding a second channel -- using transistors (!)...

I am not sure what sort of stereo you will get from 2 totally different amplifiers like that.

Looking at this thread with some interest!

On the basis that Dynatron did offer a modification to convert to stereo, we don't know as yet what that mod was. It is barely possible that it could have been to add a transistor amplifier to give two channels! Fretking seems to think that it's a workmanlike job. After all, there doesn't look as though there would be room for a second valve amp similar to the original.

Why would the stereo be less than satisfactory? All good amplifiers sound the same. And though neither the transistor amp nor the valve amp are likely to be at all cutting-edge, there probably wouldn't be enough differences between them to upset the stereo effect. It's pretty horrible to contemplate, but I'll bet it would have worked and sounded good.

[ms660]

Second amplifier?:

http://www.vintage-radio.net/forum/a...1&d=1450879627

Lawrence.

[Edward Huggins]

Yes, there it is above and referred to earlier in this Thread. This additional chassis plate carried 2 x ECL82 PP amp and took LT and HT from the main PSU. Dynatron then added in internal balance control on the top LHS on the motor board. The OP's player has clearly been "got at"!

[Fretking18]

Thanks Edward..that confirms then that this stereo modification was not done in the 60's when they would of used valve technology but in the 70's when transistor technology was the way to go ..Dynatron as a company existed till 1981..this photo shows the date that the modification was done Jan 1974 any progressive forward thinking electronics company would not be sticking with outdated technology they would be embracing the latest transistor technology as is the case here..im still convinced that Dynatron will of done this modification them selves..regardless of what some of you think ..this is definitely no bodge job this is a professionally installed part..so im going to keep it that way

[vidjoman]

Sorry but I don't think that is a professional upgrade. Nobody would leave the bridge rectifier hanging on it's wires - see your photo in post 11. It's a Mullard module added with a transformer on a metal panel. What do the controls do? If they are volume and tone, looks that way, then you will have to take the back off to adjust them. The original controls are Volume, Bass & Treble, and are mono, so there would be imbalance at any setting of the controls. It looks to be an ill thought out 'mod' done by someone without much knowledge.
It maybe that the original valve amp is faulty and someone, rather than repair it, added the transistor module to make the player work. You will have to work that one out by carefully drawing out diagrams to see what is there.

[Edward Huggins]

As many of your know, I was with Pye up to 1981 and I certainly know of no such option. The kind of people who bought Dynatrons would not add any form of "upgrade"! Even though Dynatron build quality went down during the 1970s, I cannot believe they would ever have offered an aftermarket transistor chassis to a valved product. No responsible manufacturer would have unbalanced valve and transistor amplifiers working together. Can you OP please advise, is there a single "Balance" control under the lid in the top left hand corner on the motor board?

[Collaro]

After the equipment has been disconnected, be very careful with capacitors which still may hold charge leading to high voltages!