GM70 PP

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pre65
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#136 Re: GM70 PP

Post by pre65 »

I use 6D22s damper diodes (in a hybrid bridge) on my GK-71 amp.
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Cressy Snr
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#137 Re: GM70 PP

Post by Cressy Snr »

I have a few GEC U19s (max Va 2500V) if you’re at Owston this year.
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pre65
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#138 Re: GM70 PP

Post by pre65 »

Cressy Snr wrote: Sun Feb 02, 2020 12:05 pm I have a few GEC U19s (max Va 2500V) if you’re at Owston this year.
Me too, and I also have bases and top caps. :) (NOS in boxes)
Life is what happens to you while you're busy making other plans. John Lennon

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izzy wizzy
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#139 Re: GM70 PP

Post by izzy wizzy »

Thanks for the feedback. Powering the GM70s is done and I'm happy with the 866 MVs like what was seen at Owston last year. I have spares so should be fine for the next 20 years. If not, there's always 6D22S which I have also.

It's the 4P1L front end that's the issue going forward where the RG1/250 MVs have no future. It draws 60mA at about 235V which is why I'm asking about the 4V British DH rectifiers or the 5R4GY (maybe someone has some of the these for sale?). I have no experience of these gizmos. For now, I may go SS diodes to get going like I did way back in the beginning of the 46 813.

I'd like to get this nailed before Owston and bring the revised amp along; thanks for the offers guys.
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#140 Re: GM70 PP

Post by simon »

Dunno. If you think you can hear the difference in rectifiers, not saying you can't BTW, you probably need to try 1Ns, something faster, then try the 6AX4s etc. and see what difference you do hear. There's a lot written on the net about which is best but nothing clear. I suspect it's very individual.

Well, that's a really unhelpful post!
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#141 Re: GM70 PP

Post by izzy wizzy »

Well after all that head scratching and suggestions, have got an order in for 20 6AX4GT which should keep me stocked up for this amp and the future for the line and phono. In the end didn't fancy the DH rectifier route as it would be too hard to get a decent stock and realised, I'm not a valve roller anyway.

While I wait for them and something to light them up with, I'll pop some silicon in.
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#142 Re: GM70 PP

Post by izzy wizzy »

Reckon this amplifier is all about challenging my preconceived ideas about what I want and how to go about it. Popped some UF4007 diodes to power the front end and like that a whole lot more. I've learned that the MVs I was using for this are a lot trickier than I had imagined and even if they glow blue, that doesn't mean they're working properly. More impressed with the seperate driver supply results than before.

So that leads me onto alternatives. Got an order in for 6AX4 dampers as they're cheap and seem a popular choice. Also on order are 5R4GY, 5U4G and DW4-350 as I want to hear DH rectfiers in keeping with the whole DH vibe of this amp. I can also try 6D22S instead of the MVs for the GM70s just to see what happens. I think some of the above DH jobbies will power the phono in future too.

I found some cheapish transformers at RS to light all the above rectifiers up, 6.3V and 5V ones; 5 in all for £45 delivered.
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#143 Re: GM70 PP

Post by RhythMick »

I know it's obvious, but won't the change of rectifier change the operating points of the valves? Especially changing tube to SS.

If you're really wanting to compare the sounds of rectifier circuits wouldn't you need to regulate the HV ? Maybe you already do?
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#144 Re: GM70 PP

Post by izzy wizzy »

RhythMick wrote: Sun Feb 09, 2020 5:37 pm I know it's obvious, but won't the change of rectifier change the operating points of the valves? Especially changing tube to SS.

If you're really wanting to compare the sounds of rectifier circuits wouldn't you need to regulate the HV ? Maybe you already do?
I have multi tapped HV transformers so HT will be close enough after using different taps for different rectifiers.

Changing the MVs for uf4007 resulted in a HT change of 5v-ish.

And a 5% variation in HT shouldn't radically alter the sound.... hopefully. I'm really after the one that works with what I have rather than testing to come to some universal conclusion about rectifiers.
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#145 Re: GM70 PP

Post by little eddy »

Are these an option - used in my Niobium: http://vinylsavor.blogspot.com/2012/01/ ... -6by5.html
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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#146 Re: GM70 PP

Post by izzy wizzy »

little eddy wrote: Sun Feb 09, 2020 9:27 pm Are these an option - used in my Niobium: http://vinylsavor.blogspot.com/2012/01/ ... -6by5.html
For dampers yes but I'm already invested in 6AX4 for the line/headphone amp so want to keep to same to limit variety in stock holding going forward.

Within a year, I'm going to be on the other side of the world so getting valves won't be as easy so stocking up on what I need to feed my amps now :)
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#147 Re: GM70 PP

Post by simon »

You going back home Stephen?
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#148 Re: GM70 PP

Post by izzy wizzy »

simon wrote: Mon Feb 10, 2020 12:39 pm You going back home Stephen?
After 35 years, yes. Only popped over for 6 months :D
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#149 Re: GM70 PP

Post by simon »

You'll need a shipping crate twice the size for those Tannoys :-)
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#150 Re: GM70 PP

Post by izzy wizzy »

simon wrote: Mon Feb 10, 2020 6:07 pm You'll need a shipping crate twice the size for those Tannoys :-)
Yes and accomodate them at the other end. They were only made as a test to see if I liked them but life changes and before you know it, 16 years go by. See the theme here :)

Will have to downscale a bit temporarily and leave the cabinets here. Plan is to build rectangular GRFs which will fit into the next living room.
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