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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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21st Oct 2021, 11:17 pm | #21 |
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Re: Help needed with Dynatron RG11 Berkeley
I realise you are not as experienced as some of us on here, but in the picture on post #18 there are two capacitors on either side of that leaky one, they are both suspect and need replacing.
I generally replace the following: All paper wax or moldseal capacitors (the brown ones in your picture) in the preamp/power amplifier, all resistors over 100K ohms and measure replace all other resistors. Check the resistors and capacitors in the cathode circuit of the output stage replace as necessary. Once done check each module in turn. If you don't feel confident in doing it, get someone like myself or John to do it for you. I do this type of work professionally. |
21st Oct 2021, 11:57 pm | #22 |
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Re: Help needed with Dynatron RG11 Berkeley
Old amplifiers do not age well and all the paper capacitors will be leaky and 50% of the resistors are likely to be out of tolerance. So the question becomes do you want it to work as original or look original? As you want to use this regularly leaving faulty original parts is just not worth the risk.
You will need to change all the paper capacitors just not all at once. There are 4 that need replacing in the last picture, two Hunts, one TCC paper wrapped, and one metalpac. The 'leakage' looks like a sealant that has been applied to the capacitor during production and it also appears on the capacitor in the power amplifier. At this stage you should create a list of all the parts you need. The first to replace would be the grid coupling capacitors which I think are the two I identified earlier. After each replacement you should power it up to check everything is still good. I was going to point you to a circuit diagram for the Leak TL12+ but I see this amplifier has the ECC83 phase splitter but no EF86 so I am not sure how the feedback is wired. The lack of a circuit diagram is going to be a problem. |
22nd Oct 2021, 8:26 am | #23 |
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Re: Help needed with Dynatron RG11 Berkeley
Ok this is great stuff if I’m not going for a blanket approach I will buy a capacitance tester. The pre amp/tone control unit has twin RF 86 in it? I’m assuming the phase splitter on the power amp is what splits the push and pull for the twin EL84s?
I do lots of scientific stuff at work so I’m quite enjoying learning about all this stuff all your knowledge and tips is greatly appreciated. JB |
22nd Oct 2021, 8:48 am | #24 |
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Re: Help needed with Dynatron RG11 Berkeley
You mean EF86. Yes, basically that's what the Phase-Splitter does. In some circuits it can also give a degree of gain.
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22nd Oct 2021, 9:42 am | #25 |
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Re: Help needed with Dynatron RG11 Berkeley
A capacitor tester will not measure leakage. To measure leakage you need a high voltage power supply and an oven to raise the test temperature then apply the full working voltage of the capacitor through a series resistor and measure the current. When new the capacitors would have leaked less than 1uA.
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22nd Oct 2021, 9:55 am | #26 |
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Re: Help needed with Dynatron RG11 Berkeley
A high voltage insulation resistance tester ("megger") will identify leaky capacitors, just unsolder one end before testing. Then when (most likely not if) you find leakage you're already half way to removing the duff cap!
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22nd Oct 2021, 10:04 am | #27 |
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Re: Help needed with Dynatron RG11 Berkeley
Can I use the assembled amp to check for leakage ie unsolder one end of grid coupler add an ammeter turn it on an warm it up? If disconnected one side could I observe an increase in potential on the Grid side as an indicator of leakage? I can monitor on a scope.
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22nd Oct 2021, 10:25 am | #28 |
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Re: Help needed with Dynatron RG11 Berkeley
If it's a grid coupling capacitor you can measure the voltage on the control grid wrt chassis. If it's positive the capacitor is leaky.
You can confirm this by disconnecting the capacitor from the grid and checking the voltage on the disconnected lead wrt chassis. It should be zero.
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22nd Oct 2021, 1:24 pm | #29 |
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Re: Help needed with Dynatron RG11 Berkeley
Do I test the grid couplers with the valves in or out??
Also megger at 500v/250v are 20 quid can I megger a400v cap briefly at 500? |
22nd Oct 2021, 1:35 pm | #30 |
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Re: Help needed with Dynatron RG11 Berkeley
You can test the audio coupling capacitors with the output valves in or out, so long as the valves for the previous stage aren't in the same envelope as the output valves.
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22nd Oct 2021, 3:46 pm | #31 |
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Re: Help needed with Dynatron RG11 Berkeley
Ok so all valves out power it up and check the grid pin hole voltage?
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22nd Oct 2021, 9:06 pm | #32 |
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Re: Help needed with Dynatron RG11 Berkeley
You'll need the rectifier valve to be plugged in or there'll be no HT to leak through the coupling capacitors to the control grids of the output valves.
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22nd Oct 2021, 10:07 pm | #33 |
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Re: Help needed with Dynatron RG11 Berkeley
Lol yes I suppose I might
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23rd Oct 2021, 11:19 am | #34 |
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Re: Help needed with Dynatron RG11 Berkeley
I would not recommend leaving the grid coupling capacitors even if they seem OK.
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23rd Oct 2021, 12:04 pm | #35 |
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Re: Help needed with Dynatron RG11 Berkeley
Neither would I. They'd be the first things I'd replace.
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23rd Oct 2021, 2:07 pm | #36 |
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Re: Help needed with Dynatron RG11 Berkeley
Yes I’m leaning that way to swap all HV/LV caps - although the amp seems to also have some resettable trips in it??
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28th Oct 2021, 6:16 pm | #37 |
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Re: Help needed with Dynatron RG11 Berkeley
I know I shouldn’t but ooooh shiney bits…. And after some good tips on the components page I have a steer where to go on the troublesome caps I can’t source- going to leave the old ones in place and put new ones inside the chassis as separate caps (60+100uf can’t be found as a new part… and it’s reading low).
I might go for a 60:60 and pop a 40 inside the box - still thinking…. JB |
29th Oct 2021, 1:50 pm | #38 |
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Re: Help needed with Dynatron RG11 Berkeley
Ok so I tested the gram pickup and it’s dead so I was going to follow the earlier advice of fitting a modern stereo cartridge- there are some on eBay for not much with a flip over needle do I just mount this into the existing arm? And re set the needle weight to 4 grams?? Will that work on 78s?
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29th Oct 2021, 3:27 pm | #39 |
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Re: Help needed with Dynatron RG11 Berkeley
If it is the original Garrard RC80 autochanger (please advise) then you may have some difficulty in getting this to track as low as 4 grams. Also if you are going to buy one of the cheap chinese ceramic stereo cartirdge you will need to fettle some kind of cartridge mounting. If the tone arm head is detachable (?) it will be a bit easier. It needs to be mounted at the correct tracking angle.
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29th Oct 2021, 7:38 pm | #40 |
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Re: Help needed with Dynatron RG11 Berkeley
I bought one with the mounting clip to fix into the head… also eyeing up spare head cases to keep the original one original.
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