|
Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
|
Thread Tools |
14th Jan 2017, 1:13 pm | #1 |
Heptode
Join Date: Sep 2014
Location: Coventry, West Midlands, UK.
Posts: 518
|
Regentone NINE-3 stereo radiogram
Hi Guys,
any component numbers are from the manufacturers manual. this gram has been working perfectly for 10 years since I changed the "that caps" in it until just before Christmas. Having set up the crib etc on the top it was time to play some Christmas records. Switch on it warms up start to play a record then there is a click click hum. It sounded like a valve flashing over. I left it until the Christmas things were taken down. I dread taking the chassis out of this as there are a number of wires to unsolder,speaker leads, balance control, plus its heavy and has a large glass tuning scale. I had noticed that there was no display on the tuning indicator but the heaters of all the valves were lit and there was the hum on both channels. I measured the ht and it was down to 150v instead of the 318v mentioned in the makers manual. even without the output valves in T6 output transformer was getting warm. I snipped R46 1K5ohm,cutting off the supply to the rest of the set and the transformer rapidly heated up and oozed wax. After removing the transformer I can see a couple of green spots under the windings so suspect shorted turns.With the transformer removed the voltage reading was back up to 300+v. I fitted a transformer without the choke winding and away it went working as well as it did before, I thought of fitting a spare transformer I have from an A155 chassis but it is too big. I will have to see about getting the transformer rewound. Steve |
14th Jan 2017, 1:26 pm | #2 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,302
|
Re: Regentone NINE-3 stereo radiogram
Presumably the primary of the removed OP TX had a winding used as part of the smoothing. Without this in use, is the hum level the same? Well done, a nice gram - nothing wrong with Regentones!
__________________
Edward. |
14th Jan 2017, 1:54 pm | #3 |
Banned
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
|
Re: Regentone NINE-3 stereo radiogram
Many of these chassis with a tapped primary output tranny will work perfectly well without it.
I had the same problem with a Bush but that one hummed slightly with an ordinary tranny so I managed to wind a bit of a over winding onto the bobbin without taking it apart, worked fine then. Think I used 36 swg enameled. I don't think it makes a lot of difference if its not wound the same way as the primary unless I was just lucky. |
14th Jan 2017, 5:24 pm | #4 |
Heptode
Join Date: Sep 2014
Location: Coventry, West Midlands, UK.
Posts: 518
|
Re: Regentone NINE-3 stereo radiogram
the gram works perfectly without that over wind. but woulld like to get the original transformet rewound so as to keep it as original as pos.I think the short must be to chassis as even without the valve and nothing coming off the tap it still overheated.
What I did find due to this happening was that when I replaced the original smoothing and reservoir caps I somehow forgot to replace the 2 8uf electrolytics C55 and C56 now on FM with those in place the reception is much better and the "magic eye" closes on strong stations something it never did before Just played Sade "Smooth operator" sounds damn good even if I do say so. Using a magnetic ADC QLM30 mkIII cartridge in the UA14 via an off the shelf preamp and into a pair of Dynatron spkrs and another pair just on baffle boards robbed from an old German radiogram. Steve |
14th Jan 2017, 10:35 pm | #5 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,302
|
Re: Regentone NINE-3 stereo radiogram
An ADC QLM30 in a BSR UA14 - that's very brave of you. I'd just love to hear this set up. Note the output impedance of your Regentone is just 3 ohms, so be careful of that multi speaker matching.
__________________
Edward. |
15th Jan 2017, 12:01 pm | #6 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
|
Re: Regentone NINE-3 stereo radiogram
If the Regentone amplifier is a reasonable design, its OUTPUT impedance will be considerably less than 3 ohms. However it will be intended to drive a LOAD impedance of 3 ohms.
Audio output stages are designed for the best compromise between output power and distortion in the mind of the designer (or at any rate the valve manufacturer) and this is very unlikely to involve anything like matched output and load impedances.
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
16th Jan 2017, 12:16 am | #7 | |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
|
Re: Regentone NINE-3 stereo radiogram
Quote:
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments. |
|
16th Jan 2017, 1:45 am | #8 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
|
Re: Regentone NINE-3 stereo radiogram
Yes impedance match for best power transfer is true, but not necessarily for lowest distortion. A half decent amp with reasonable feedback, though, has its output impedance lowered by the action of the feedback. This has benefits including damping of speaker resonances. The output impedance of a good valve amp will be about 1/10 of the speaker nominal impedance. (For solid state it may be as low as 1/1000).
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
16th Jan 2017, 1:49 am | #9 | |
Dekatron
Join Date: Aug 2006
Location: Madrid, Spain / Wirral, UK
Posts: 7,484
|
Re: Regentone NINE-3 stereo radiogram
Quote:
There is a little metal adaptor plate with a single top hole then two half-inch protrusions that was supplied with many BSR and Garrard decks in the 60s, so it's actually quite easy to fit such carts. Haven't got a pic unfortunately. Well, Autochangers and magnetic carts: it can be done. I have several autochangers with magnetic carts. Garrard 40B, BSR MA70, BSR C142 and Dual 1225. That said, those decks all have counterbalanced arms and antiskate, so perhaps I'm cheating a bit!
__________________
Regards, Ben. |
|
16th Jan 2017, 2:25 pm | #10 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
|
Re: Regentone NINE-3 stereo radiogram
I don't think you can apply passive network power transfer theory to active systems like a valve amplifier. You can change the output impedance simply by adding negative feedback!
|
16th Jan 2017, 9:33 pm | #11 | |
Triode
Join Date: Dec 2015
Location: Les Salles Lavauguyon, France
Posts: 43
|
Re: Regentone NINE-3 stereo radiogram
Quote:
https://en.wikipedia.org/wiki/Maximu...ansfer_theorem For audio efficiency you'd probably want the source to be as low as possible, including the speaker wiring, since the source has also to sink power to control the loudspeaker excursions. Scaling it up, the last thing you want is a 500MW power station generator matched to its load, 250MW of dissipation would be devastatingly exciting. R. |
|
5th Feb 2017, 12:51 pm | #12 |
Heptode
Join Date: Sep 2014
Location: Coventry, West Midlands, UK.
Posts: 518
|
Re: Regentone NINE-3 stereo radiogram
just a note to those who have said they would like to hear this. I had to have the man from Virgin out as a plant had become top heavy and overnight toppled over pouring the contents of the plant pot holder into the tivo box,oops. I had the radiogram on when he arrived and he thought it was surround sound. I felt quite chuffed to say the least. He was also intrigued when setting the box up on the Regentone 17-18 tv I think he got a bit educated lol
Steve |