Valve amplifier issues... Help Please

[electrogram]

I have one of these players, havn't actually seen it for a while, in the roundtuit pile, with the other chanel extra valve amp fitted. The controls on the front are twin gang for Stereo, I assume you got that whether you you specified mono or stereo when bought new. The requirements for a power supply for two as opposed to just one amplifier are hugely disparate, if you bought a mono player and later upgraded to Stereo did you get a bigger mains transformer fitted too? If not you would think HT voltage would be considerably reduced

[JacKam_]

Too much unknown variables in this equation, but simple experiment would help :

1. Measure HT voltage and max current that this circuit draws.
2. Check the max current available from the rectifier valve.

If it can handle twice as much :

3. Add voltage dropper in parallel, to get the current twice as much as without the dropper.
4. Measure HT voltage again and sound quality.
5. Check the transformer temperature. Power off if too hot.

J

[Fretking18]

Originally Posted by Collaro

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

Thank you for this bit of advice which i will of course follow

[AC/HL]

From this post: http://www.vintage-radio.net/forum/s...40&postcount=1
It would appear that there were at least two versions of the GR4, the SA and ST. Presumably they both had ganged controls and adequate power capacity, the SA just lacking the sub chassis, as with convertible TVs. I'm inclined to agree with Kalee20 that with matching speakers it would produce reasonable stereo reproduction for it's market position. Also with the majority that this was not a Dynatron modification, although it is quite workmanlike, by no means a rough bodge. Does anyone know of a straight GR4 without a suffix?

[Fretking18]

Originally Posted by electrogram

I have one of these players, haven't actually seen it for a while, in the roundtuit pile, with the other channel extra valve amp fitted. The controls on the front are twin gang for Stereo, I assume you got that whether you you specified mono or stereo when bought new. The requirements for a power supply for two as opposed to just one amplifier are hugely disparate, if you bought a mono player and later upgraded to Stereo did you get a bigger mains transformer fitted too? If not you would think HT voltage would be considerably reduced

Hi Electrogram

it looks like this until was originally bought as a mono unit but was upgraded in 1974 to stereo, it was wired for a stereo cartridge, the second power amplifier has its own power transformer but was created using transistors rather than valves..

[Fretking18]

Originally Posted by JacKam_

Too much unknown variables in this equation, but simple experiment would help :

Thank you for this valuable advice...but i now have it working not just in Mono but in Stereo too and have put it all back into the case it came in so i wont be doing any more testing on it.

[Fretking18]

Originally Posted by AC/HL

Does anyone know of a straight GR4 without a suffix?

HI Bill

I have a copy of the Dynatron owners Manaual which states that there were only two models the GR7SA (stereo adaptable model) and the GR7ST (Stereo Model)

[ColinTheAmpMan1]

Originally Posted by kalee20

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.

I have to disagree with your statement that "all good amplifiers sound the same" - why are some fairly reasonably priced (NAD 3020) and some much higher priced (Leak and Quad)? Linearity, total harmonic distortion, bandwidth, power bandwidth, transient response and recovery and such all count for something, surely? Please don't take me for an audiophool, but there must be a difference between "budget" quality and "top of the range" equipment.

I think you may be overlooking something. Stereo isn't just simply two channels of sound, things such as phase differences are pretty important. If the two channels are not as identical as they can be, you will get all sorts of equalisation and phase-differences, which would mean that the stereo image could be hopelessly compromised. In my younger days, I tried listening to stereo vinyl using an Armstrong receiver on one channel and an RSC 20-watt ultra-linear push-pull amplifier on the other. The loudspeakers were totally different, too. To my uneducated rag ears, it sounded ok at the time, but then I didn't really know what stereo was supposed to sound like. So yes, it would have "worked" and "sounded good" to someone like my youthful self, but that still doesn't make it proper stereo "like it oughta be".

Colin.

[TonyDuell]

Please check your attributions, I never said that all amplifiers sound the same. In fact I implied that one channel on a valve amplifier and the other on a transistor amplfiier might well not sound that good. As far as I know all 'reasonable' stereo systems had identical amplifiers for the 2 channels.

That said, Philips sold a little transistorised preamplifier for some of their 4 track tape recorders. One use was to allow the playback of stereo tapes. You played track 1 (left channel) through the tape recorder and track 3 (right channel) through this preamplfiier and your radio (feeding the signal into the pickup sockets on the latter). No way are those 2 amplifiers going to be the same. But I guess it was better than nothing.

[AC/HL]

Attribute corrected, yours was a quote within the post.

[julie_m]

An ideal valve amplifier and an ideal transistor amplifier would sound the same. However, we are talking about real amplifiers which deviate from ideal behaviour -- and different technologies can be expected to deviate from the ideal in different ways. In practice, valve amplifiers tend to produce distortion mainly in the form of low harmonics (nothing beyond the 5th) whereas transistor amplifiers tend to produce distortion mainly as odd harmonics at low levels, but spead all the way up the audible spectrum.

A transistor amplifier with a lower THD figure than the valve amplifier would produce less of the objectionable high harmonics, and probably would sound similar enough in practice. My personal experiments with heterogeneous stereo suggested that some mis-matching was quite acceptable for most sources, with a few exceptions.

[Nickthedentist]

Interesting thread.

Yes, this is a stereo-adaptable machine from the early 1960s that someone's adapted to stereo at a much later date using a neat, home-made, solid-state, amp instead of the Dynatron LF18/ST which it was intended to accept.

Your four choices would seem to be to look for an original LF18/ST (good luck with that!), make up your own LF18/ST copy, keep it as-is and tidy up the dangling rectifier etc., or remove the added stuff and get it back to its original mono-but-adaptable-for-stereo state.

Personally, I would leave the addition in place. It would be easy enough to remove later should the urge take you.

N.

[Nickthedentist]

Manufacturer's data available here: http://www.service-data.com/product....03/1802/m11303

[Nickthedentist]

And this is what the original bolt-on module would have consisted of, i.e. two valves, and output transformer and a handful of passive components:

[ColinTheAmpMan1]

Originally Posted by TonyDuell

Please check your attributions, I never said that all amplifiers sound the same. In fact I implied that one channel on a valve amplifier and the other on a transistor amplfiier might well not sound that good. As far as I know all 'reasonable' stereo systems had identical amplifiers for the 2 channels.

I apologise for my poor editing. Yes, it was Kalee who I was disagreeing with and not you, Tony. I think we are actually in total agreement! Also, thanks to AC/HL for correcting my error.

Colin.