It is clear that for the direct coupled with stacked power suply are necessary the same power supply of the interstage version, no more.
In my case:
170-180v for the driver stage
90-130v variable for the bias of GM70
1000v for the output stage
I cannot see problem of this configuration.
The cost is reduced because there is a simple anodic choke instead of an expensive interstage and the frequency band depend only by the output transformer if the choke have enough inductance.
The interstage transformers are complex components with more problems and frequency band limitation than output transformers.
I think to try it soon using a pair of sowter 8982 Plate Choke with
100 Henry 50 mA and about 300ohm
In my case:
170-180v for the driver stage
90-130v variable for the bias of GM70
1000v for the output stage
I cannot see problem of this configuration.
The cost is reduced because there is a simple anodic choke instead of an expensive interstage and the frequency band depend only by the output transformer if the choke have enough inductance.
The interstage transformers are complex components with more problems and frequency band limitation than output transformers.
I think to try it soon using a pair of sowter 8982 Plate Choke with
100 Henry 50 mA and about 300ohm
audiodesign said:
I never had problems at the startup, I use mercury rectfiers that are pretty fast in reaching the B+.
You can trim Rx to adjust the bias of the output tube while the driver ages. Anyway I never touched it in months.
audiodesign said:
Where? Dunno. I believe this is a very old idea. Probably the first instance was a 6C45/300B design described here on DIY. But the original idea is much-much older. Nothing new for tubes.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=73513&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=42477&highlight=
Here pics, schematics and measurements of the amps I built. You will see many many tubes including GM70. I have settled now with 75TLs. That's an italian forum, what else? 
Copper vs graphite: I liked copper GM70s. On the other hand I liked graphite 813s. As far as I know there is no reason why copper should be better, for sure they are too pricey.
I see GM70s on a regular basis on Ebay. Including copper anodes.
Copper vs graphite: I liked copper GM70s. On the other hand I liked graphite 813s. As far as I know there is no reason why copper should be better, for sure they are too pricey.
I see GM70s on a regular basis on Ebay. Including copper anodes.
At the startup the direct coupled with dropping resitor can give problema because the warm time of the D3a could be more longer than GM70 so this can be destroy for the low Vg.
The direct coupled without dropping resistor (in the attach second schematic) give the same peformance of the other solution but it is sure in any condition, also if the D3A is not in the socket.
It is obvious that this solution cannot be applied in my 845 with 2 tube stage ampl. (see other forum) because 1000+120+1000 = 2120 voltage of isolation are too much for any output transformer.
The direct coupled without dropping resistor (in the attach second schematic) give the same peformance of the other solution but it is sure in any condition, also if the D3A is not in the socket.
It is obvious that this solution cannot be applied in my 845 with 2 tube stage ampl. (see other forum) because 1000+120+1000 = 2120 voltage of isolation are too much for any output transformer.
Attachments
Hi boys,
it seems an Italian affair!!!!!!!!!!!!!!
I hope that the information will help to understand the projects.
I am living in the same city of Andrea (Roma), today I phoned him to speak about the schematics. I invited him to have a match between the s.e. (that I not consider a good choice and I abandoned years ago) who Andrea built, with some pp I made during last time, ma.nly with 300B, the best.
I wrote some article on Audioreview (www.audioreview.it), the most important hifi magazine in Italy (and maybe in the world mainly for the high quality of his lab, very complete).
Just to understand:
http://www.multitask.it/diy/300B-1.JPG
there is a prototype of a pp of 300B with a particula out. trafo; 1.300 uF of cap; separate toroid for filaments, ecc.
20w at 8ohm and 30 at 4 ohms (!); bw 2Hz-60KHz open loop;
here:
http://www.multitask.it/diy/fabfour.jpg
a first pair of double pp of 300B I made (Fab Four);
45 w at 8 ohm, 65w at 4 ohm rms; BW 2Hz-70 Khz open loop, 160Khz with 6 dB of FB.
here:
http://www.multitask.it/diy/1000enium.JPG
the last version of double pp of 300b; the total cap. is 2500 uF at 500 Vdc; the power in rms is similar to the previous one but dinamically is better; the frq. response is little bit better.
The transformer are customa made, double C; two separate secondary at 3 ohm each (in parallel); 30Kg each.
Building a S.e. is less complicated to build a pp and this is the challenge I am following; I believe that the sonic caratheristi are much better than s.e. mainly if the 300B is used; this only if connencted at the right trafos.
I forgot to mention a EL34 monos (eight EL34 per channe):
http://www.multitask.it/200w/1.jpg
it is possible to configure it in triode, UL and pentode mode.
In triode are 110w, in UL about 170w, in pentode close to 200 w.
The iron I used are only custom and very expensive.
Ciao ( for the moment)..
Walter
it seems an Italian affair!!!!!!!!!!!!!!
I hope that the information will help to understand the projects.
I am living in the same city of Andrea (Roma), today I phoned him to speak about the schematics. I invited him to have a match between the s.e. (that I not consider a good choice and I abandoned years ago) who Andrea built, with some pp I made during last time, ma.nly with 300B, the best.
I wrote some article on Audioreview (www.audioreview.it), the most important hifi magazine in Italy (and maybe in the world mainly for the high quality of his lab, very complete).
Just to understand:
http://www.multitask.it/diy/300B-1.JPG
there is a prototype of a pp of 300B with a particula out. trafo; 1.300 uF of cap; separate toroid for filaments, ecc.
20w at 8ohm and 30 at 4 ohms (!); bw 2Hz-60KHz open loop;
here:
http://www.multitask.it/diy/fabfour.jpg
a first pair of double pp of 300B I made (Fab Four);
45 w at 8 ohm, 65w at 4 ohm rms; BW 2Hz-70 Khz open loop, 160Khz with 6 dB of FB.
here:
http://www.multitask.it/diy/1000enium.JPG
the last version of double pp of 300b; the total cap. is 2500 uF at 500 Vdc; the power in rms is similar to the previous one but dinamically is better; the frq. response is little bit better.
The transformer are customa made, double C; two separate secondary at 3 ohm each (in parallel); 30Kg each.
Building a S.e. is less complicated to build a pp and this is the challenge I am following; I believe that the sonic caratheristi are much better than s.e. mainly if the 300B is used; this only if connencted at the right trafos.
I forgot to mention a EL34 monos (eight EL34 per channe):
http://www.multitask.it/200w/1.jpg
it is possible to configure it in triode, UL and pentode mode.
In triode are 110w, in UL about 170w, in pentode close to 200 w.
The iron I used are only custom and very expensive.
Ciao ( for the moment)..
Walter
Walter,
push pull or single ended ?
Many years ago I have built this project:
http://www.audiodesignguide.com/my/pp3a.gif
I have called 2 my friends piano musicians and they have ear this amplifier in normal conditions and with one kt88 grid connected to ground.
If I connect one kt88 grid to ground the amplifier is transformed to a single ended.
So, both are prefered this in single ended also if the power was lower.
They have considered the single ended more natural so more near to real sound.
push pull or single ended ?
Many years ago I have built this project:
http://www.audiodesignguide.com/my/pp3a.gif
I have called 2 my friends piano musicians and they have ear this amplifier in normal conditions and with one kt88 grid connected to ground.
If I connect one kt88 grid to ground the amplifier is transformed to a single ended.
So, both are prefered this in single ended also if the power was lower.
They have considered the single ended more natural so more near to real sound.
audiodesign said:
I built monoblocks. 40kg each ... sob
Google bottom audio for pics and description on our italian forum.I have two switches for the PSUs: one for low voltage, the other for high voltage. As a matter of facts I turn both on at the same time and I had no problems at all in all the DC amps I built. You could use a delay on the higher PSU for safety.
Italians pizza spaghetti mandolino and tube amps that can kill you?
Ebay ? I don't know what are you talking about.. javascript:smilie('')
I was looking for matched pairs or at least some testing, any NOS on-line shop?
What kind of separation do you mean is required? just LC or bridge+LC or dual mono ? Do you think that channels L-R intermodulation could be worste than in normal topology ?
In Audioreview magazine of February there's the last Esoteric amplifier: It's a very very advanced PP amp (KT88) costing 15.000€. Sound? Awwwwwesome..
Rout 5ohm on 8ohm ( with feedback )
hehehehe isn't it funny ?javascript:smilie('') There's an andvanced microcontroller that control bias but it crash every time and they had to reboot like windows 98..hahaha
It surely mean nothing but i think it's funny
Ebay ? I don't know what are you talking about.. javascript:smilie('
')I was looking for matched pairs or at least some testing, any NOS on-line shop?
What kind of separation do you mean is required? just LC or bridge+LC or dual mono ? Do you think that channels L-R intermodulation could be worste than in normal topology ?
In Audioreview magazine of February there's the last Esoteric amplifier: It's a very very advanced PP amp (KT88) costing 15.000€. Sound? Awwwwwesome..
Rout 5ohm on 8ohm ( with feedback )
hehehehe isn't it funny ?javascript:smilie('
') There's an andvanced microcontroller that control bias but it crash every time and they had to reboot like windows 98..hahahaIt surely mean nothing but i think it's funny
For Gluca:
there is a big differences between the schematic you sent from Andrea's one.
On your example the cathode is not bypassed so, in this case the V3 is modulated from the ac voltage on R6.
On Andrea's the cathode of KT88 is bypassed so there isn't modulation and the KT88 is not working in ac.
Ciao
WG
there is a big differences between the schematic you sent from Andrea's one.
On your example the cathode is not bypassed so, in this case the V3 is modulated from the ac voltage on R6.
On Andrea's the cathode of KT88 is bypassed so there isn't modulation and the KT88 is not working in ac.
Ciao
WG
Yes, this is true the two schematic are very different
in the Gianluca version the second tube give some contribution on output because also if this have the grid connected to ground it receive a parts of signal from the cathode.
in my case if I connect one grid to ground the second tube is near to a fix costant current generator so this will give a sound like a single ended configuration.
in the Gianluca version the second tube give some contribution on output because also if this have the grid connected to ground it receive a parts of signal from the cathode.
in my case if I connect one grid to ground the second tube is near to a fix costant current generator so this will give a sound like a single ended configuration.
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