Mr Liang

Hi.
With thanks to Andrew for supplying the tubes I have converted my amp to gm70 outputstage.After switch on and testing I am mighty impressed,there is now much more impact to the sound,I can now understand why Mr I didnt like the sound of this amp, it was to anaemic sounding with the 845 tubes.This is definately a must for anyone with a Liang ,just needs 18 0 18 heater supply and uprated smoothing caps for heater supply,I used 44000uf.Also needs new sockets for gm70.If anyone needs sockets dont get them off the guy on e bay advertising sockets and tubes combined he sent two odd tubes and would not sort the mistake out; he said I was seeing things and that both tubes were the same.One was a copper plate the other graphite ,guess which one turned out to be faulty?I will post photos If I can find out how to.
Regards Dave.

[bonneville]

When Dave invited me over to see his Gm modifications I had visions of some genetically modified plants tucked away in his greenhouse, however it turned out to be the latest incarnation of his Mr Liang .I did notice it had sprouted a extra can on the rear which he explained was a transformer for heaters but the bulk of the work was concealed beneath the surface.
We tested the results on several types of speaker from Daves open baffles with the excellent green Saba tweeters & mids to vintage Wharfedale E70's and the huge Goodmans that sit in the corners of his room.
I must say I was very impressed ,and for once Dave himself who is usually hard to please was soon toe tapping along with the music.I myself had a standard Liang some time ago but this version certainly put that one to shame.
The acid test will come of course when Swampy gives it the once over,

[andrew ivimey]

Mr I has indeed done a few things to GM70s that has made them bleed if not actually anaemic, but yes, with the right heaters The Mr Lianng may sing to a different hymn sheet.

I actually like the graphite GM70s a) because they are dead cheap, b) who cares if you exceed the specs <I admit, this isn't easy> and c) they can sound very deep, full and very powerful. Even at around 9watts where my experiments began they definitely sounded better than yer average 300B.

The acid test is not Mr Swampy but to let us hear it at the next Owston!

[pre65]

Hi Dave, thanks to your interesting experiment i am now thinking of trying GM70 in place of 845 in my power stage.

What HT voltage and cathode resistor / cap are you using ?

Andrew I has found me a couple of valves so what bases are recommended ?

Hi Phillip
I am using gm70 bases off the guy on E bay called Qro stuffstores but he doesnt seem very reliable the gear took 8 weeks to arrive and one tube was faulty.The ht is probably about 900volts and the circuit is standard Liang with 18 0 18 volts 200watt toroid heater supply.The bias is user adjustable on the liang so I set this to 110 ma.It appears that 845 are becoming hard to get hold of so this seems an ideal time to change to gm70.The amp sounds far better with these tubes than 845.
regards Dave

[Tweeky]

Hi,
The words deep, full, and powerful have been used to describe the sound of the sound of the GM70. In terms of ambience and detail, how do they compare to the metal plate 845? Other than changing the valve bases, is it simply a case of changing the transformer for the heaters?

Thanks

Steve

Hi Steve.
The output stage and 845 bases just unplug from Mr liang ,I then duplicated the ciruit by hardwiring it to the gm70 bases which I drilled and tapped the Liang top plate to accept.I would say this mod sounds better than the standard Liang fitted with 845 metal plate tubes which Avinash has.You will need 18 0 18 transformer for heater supply and higher rated voltage wise smoothing caps for this supply.The Liang in 845 guise never sounded "right " to me and I tried various cicuits ,ie Lampizator and the Austrian guys mods but ,running gm70 its as if some sort of distortion has been removed from the sound and it is now far less annoying to listen to .
Hope this Helps .Dave.

[Tweeky]

Dave,
Thanks for your help. If I used Tentlab modules for the heaters, would I need 20-0-20 transformers rather than 18-0-18? I currently use these for both the 300B and 845 heaters and they make a big difference to the hum levels? Also, what VA rating transformers would I need?

Thanks

Steve

Hi Steve.
I dont know about the tentlab modules but I used crc of 22000uf 0.1 ohm22000uf with a 0 18,0 18 volt 250 va toroid and there are no problems with hum.
Hope this helps, Dave.

[andrew ivimey]

Me too Dave, buuuuuuuuuuuut the toroids did get hot! (small price to pay for that powerful sound though.