Tim,
I had a good look at some data sheets for lower power MOSFETs.
As long as you maintaing greater than 25V across Drain to Source at all times then the capacitances are low and hardly vary. The ZVN0545A was chosen because it has low device capacitances anyway. It is a small 600mW "E-Line" device. Larger MOSFETs will have larger capacitances.
So If we assume that the source (which drives the EL84 grid1) will swing up to 0V then as long as the +ve rail to the drain is at least +25V there should not be significant problems. I'm using 56V (that rail marked +75V is actually +56V). That is plenty.
On these monoblocks I just don't have space or heater supply capacity for another tube, let alone two, so the source follower will stay (appologies Allen, I can't do things "properly" in this instance) and I will probably leave it arranged as currently shown but will try to up the current a bit.
Its 10 minutes to knock off time Friday will advise any further advances (f any) Monday.
Also the cleaning lady will have been this arvo while I'm at work and she always leaves a review of the latest amp mod. 2nd opinions are always valuable. It wouldn't be the first time I got home Friday evening to find a note saying "put it back the way it was last week".
Cheers,
Ian
I had a good look at some data sheets for lower power MOSFETs.
As long as you maintaing greater than 25V across Drain to Source at all times then the capacitances are low and hardly vary. The ZVN0545A was chosen because it has low device capacitances anyway. It is a small 600mW "E-Line" device. Larger MOSFETs will have larger capacitances.
So If we assume that the source (which drives the EL84 grid1) will swing up to 0V then as long as the +ve rail to the drain is at least +25V there should not be significant problems. I'm using 56V (that rail marked +75V is actually +56V). That is plenty.
On these monoblocks I just don't have space or heater supply capacity for another tube, let alone two, so the source follower will stay (appologies Allen, I can't do things "properly" in this instance) and I will probably leave it arranged as currently shown but will try to up the current a bit.
Its 10 minutes to knock off time Friday will advise any further advances (f any) Monday.
Also the cleaning lady will have been this arvo while I'm at work and she always leaves a review of the latest amp mod. 2nd opinions are always valuable. It wouldn't be the first time I got home Friday evening to find a note saying "put it back the way it was last week".
Cheers,
Ian
Ian,
>(appologies Allen, I can't do things "properly" in this instance)<
Using even a MOSFET bootstrap will sound better than no bootstrap, certainly. Just nowhere near as good as using a tube.
Joe in Sydney (02 9607 4650) has used a darlington bipolar bootstrap with good results, better than the MOSFET.
REgards, Allen (Vacuum State)
>(appologies Allen, I can't do things "properly" in this instance)<
Using even a MOSFET bootstrap will sound better than no bootstrap, certainly. Just nowhere near as good as using a tube.
Joe in Sydney (02 9607 4650) has used a darlington bipolar bootstrap with good results, better than the MOSFET.
REgards, Allen (Vacuum State)
this thread has caught my imagination. This will be my first speaker valve amp (I have built several headphone valve amps).
I have ordered the iron from bluebelle audio (uk hammond distributor). Juts like to say Phillip from bluebell is the most helpful man i have ever come across - seriously good customer service. His last words were "i am on the phone for advice until 10pm every night."
I have 2 1650E opt's
a 370hx (550 ct, 200ma)
a 5h 200ma choke
and a steel enclosure, 17 *10.
Really looking forward to this, thanks to gingertube for the design.
I have ordered the iron from bluebelle audio (uk hammond distributor). Juts like to say Phillip from bluebell is the most helpful man i have ever come across - seriously good customer service. His last words were "i am on the phone for advice until 10pm every night."
I have 2 1650E opt's
a 370hx (550 ct, 200ma)
a 5h 200ma choke
and a steel enclosure, 17 *10.
Really looking forward to this, thanks to gingertube for the design.
Well, my huey monoblocks have been built for awhile, so I finally got around to taking a few photos.
These are my first amp build. I have built several speaker projects in the distant past, but no amps.
These are my first amp build. I have built several speaker projects in the distant past, but no amps.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Weekend report
I was very pleased to get home Friday and see that the cleaning lady left a review of the amps with the latest mods (current source loaded source follower at higher current) saying "MUCH Better" (her capitalisation).
No progress on the weekend - or progress of a different type.
Friday I picked up a pair of Hammond 1608 Output Transformers to resurrect the original Baby Huey - so I now have the 2 versions running and can do direct A/B tests. This confirmed that the fixed bias version is better but the original with the currect source biasing of the output tubes is very good.
As I said about 4 posts back, on the fixed bias version I have moved the shunt feedback pick offs from the output tube anodes to the ultralinear taps. I'm not 100% convinced about this mod yet. One of the things I have always tried is fitting zobels on the output transformer secondary (usually 10 Ohms + 2u2 across the 4 Ohm tap) to smooth the speakers impedance vs frequency curve. With the shunt feedback from the EL84 anodes I never found that this made much difference and so left the zobels off. With the shunt feedback from the Ultralinear taps the zobels make a significant difference confirming that some of the reflected impedance is now inside the feedback loop.
Anyone tried this mod? No .. I guess I'll have to back it out and check myself. When I first put it in I thought detail was a bit better but that was before I fixed up the source follower. Fixing the source follower made a huge difference and so I should be able to better tell if the shunt feedback pickoff point mod is worthwhile or not.
Oh! and I also I finished the Snakeskin Tolex covered guitar speaker box for my mate Neale, to go with the guitar amp I finished for him nearly 12 months ago - progress indeed.
Allen - I'll keep that Darlington Bipolar Bootstrap trick in mind. It would be nice to get rid of that extra +ve rail. I'll give Joe an email to see what devices he suggests, the required >300 Volt rating will restrict the choice a lot. BTW I use a JLTi Phono Preamp on the system, without giving too much away it is the one with the obsolete Analog Devices "Diamond" part with the the part number ground off ( A practice I understand but it really annoys me, it took me at least 20 minutes to work out what that part was, well what I think it is anyway).
Cheers,
Ian
I was very pleased to get home Friday and see that the cleaning lady left a review of the amps with the latest mods (current source loaded source follower at higher current) saying "MUCH Better" (her capitalisation).
No progress on the weekend - or progress of a different type.
Friday I picked up a pair of Hammond 1608 Output Transformers to resurrect the original Baby Huey - so I now have the 2 versions running and can do direct A/B tests. This confirmed that the fixed bias version is better but the original with the currect source biasing of the output tubes is very good.
As I said about 4 posts back, on the fixed bias version I have moved the shunt feedback pick offs from the output tube anodes to the ultralinear taps. I'm not 100% convinced about this mod yet. One of the things I have always tried is fitting zobels on the output transformer secondary (usually 10 Ohms + 2u2 across the 4 Ohm tap) to smooth the speakers impedance vs frequency curve. With the shunt feedback from the EL84 anodes I never found that this made much difference and so left the zobels off. With the shunt feedback from the Ultralinear taps the zobels make a significant difference confirming that some of the reflected impedance is now inside the feedback loop.
Anyone tried this mod? No .. I guess I'll have to back it out and check myself. When I first put it in I thought detail was a bit better but that was before I fixed up the source follower. Fixing the source follower made a huge difference and so I should be able to better tell if the shunt feedback pickoff point mod is worthwhile or not.
Oh! and I also I finished the Snakeskin Tolex covered guitar speaker box for my mate Neale, to go with the guitar amp I finished for him nearly 12 months ago - progress indeed.
Allen - I'll keep that Darlington Bipolar Bootstrap trick in mind. It would be nice to get rid of that extra +ve rail. I'll give Joe an email to see what devices he suggests, the required >300 Volt rating will restrict the choice a lot. BTW I use a JLTi Phono Preamp on the system, without giving too much away it is the one with the obsolete Analog Devices "Diamond" part with the the part number ground off ( A practice I understand but it really annoys me, it took me at least 20 minutes to work out what that part was, well what I think it is anyway).
Cheers,
Ian
Hi,
I hope this is relevent
http://www.audioxpress.com/magsdirx/ax/addenda/media/jung2778.pdf
http://www.audioxpress.com/magsdirx/ax/addenda/media/jung2779.pdf
Cheers
I hope this is relevent
http://www.audioxpress.com/magsdirx/ax/addenda/media/jung2778.pdf
http://www.audioxpress.com/magsdirx/ax/addenda/media/jung2779.pdf
Cheers
I've got two Hammond 1620 output transformers sitting around unused. I think someone here built a Baby Huey out of them? The comment was that the 6.6K primary impedance isn't quite optimal, but it should work OK. Was there anything further to report?
I'd like to make a pair of monoblocks. I have several small pieces of aluminium plate, about 9.2" by 5.8". I'm hoping I can fit one Hammond along with a suitable power transformer on each plate. Has anyone tried an Allied 6K56VG for the power transformer? I'm concerned the 540VCT winding is going to give too high B+. Is there a more economical choice? The Allieds are $45 a piece.
I'd like to make a pair of monoblocks. I have several small pieces of aluminium plate, about 9.2" by 5.8". I'm hoping I can fit one Hammond along with a suitable power transformer on each plate. Has anyone tried an Allied 6K56VG for the power transformer? I'm concerned the 540VCT winding is going to give too high B+. Is there a more economical choice? The Allieds are $45 a piece.
Ty: I used hammond 270EX transformers (275-0-275 @ 125ma) for my monoblock hueys. With the original huey PS design, my B+ was a little high (about 380V IIRC).
I ended up (per Gingertube's recommendations) with a CLC using 5uf-8H-220uf to get the B+ down to 320V. Changing the first cap value allowed dialing in the B+ within a good range. Including the 100uf at the center tap of the output transformer I suppose it would be a CLCC. My actual B+ was about 10-15V higher than my PSUDII models.
I suppose that you could also use tube rectification to reduce B+
I ended up (per Gingertube's recommendations) with a CLC using 5uf-8H-220uf to get the B+ down to 320V. Changing the first cap value allowed dialing in the B+ within a good range. Including the 100uf at the center tap of the output transformer I suppose it would be a CLCC. My actual B+ was about 10-15V higher than my PSUDII models.
I suppose that you could also use tube rectification to reduce B+
I'm new to valve poweramps, can anyone tell me if there is anything wrong with this PSU? my only fear is the model shows a large inrush current through the choke (upto 1a) which is bigger than its rating..200ma. will it survive?
An externally hosted image should be here but it was not working when we last tested it.
I just modelled (and played around a little) with your PSUDII design and it seems fine to me. If you are building a baby huey stereo I would use 200ma load, or 100ma load for monoblocks. This brings the steady state voltage down a little, actually right about where you want to be for the BH design. (I believe anything between around 300-350V B+ will work OK according to this thread)
My monoblock 8H chokes are rated for 100ma and they are doing just fine. The inrush current is very transient and short duration; the choke is just a coil of wire, so it will handle the inrush no problem, as it doesn't have much time to heat/overheat. If chokes are subjected to steady state currents exceeding their current ratings, their inductance drops precipitously also.
The PS model appears to be slightly overdamped, which, depending on your design philosophy, may be a good or bad thing. The inrush current will go down if you reduce the size of the second cap a bit. Adjusting the size of that second cap also affects damping of the ps (I just made it 220uf and there is a little overshoot on startup)
My monoblock 8H chokes are rated for 100ma and they are doing just fine. The inrush current is very transient and short duration; the choke is just a coil of wire, so it will handle the inrush no problem, as it doesn't have much time to heat/overheat. If chokes are subjected to steady state currents exceeding their current ratings, their inductance drops precipitously also.
The PS model appears to be slightly overdamped, which, depending on your design philosophy, may be a good or bad thing. The inrush current will go down if you reduce the size of the second cap a bit. Adjusting the size of that second cap also affects damping of the ps (I just made it 220uf and there is a little overshoot on startup)
Yvesm said:
Good point. Is the design goal to get close to critically damped or is overdamped OK??
Adamus: To check the "stepped" load, open the constant current box in PSUD, check the "stepped load" box, and change the current by 30-40 ma (up or down) or so and check for ringing. Make sure the step occurs after the initial voltage rise time, like 3 seconds or more (you want the voltage to be done rising when the step occurs). check for ringing/overshoot during the current change; you don't want any ringing.
Thanks for the advice, looks good to me, no ringing.
IT suggests my volatge will be a bit low (just touching 300v) but given everyones experience of psud giving a low reading that actual, i reckon 320 will be the result.
The 6.8uf is an obbligato oil cap, and the 220 will be a standard 500vdc electolytic.
Another question, i want to make a dummy load which i'll use for other builds, can i assume a 10ohm thick film will be fine for this, the electorics store doesnt have 8ohm, unles wirewound which i assume are too inductive.
IT suggests my volatge will be a bit low (just touching 300v) but given everyones experience of psud giving a low reading that actual, i reckon 320 will be the result.
The 6.8uf is an obbligato oil cap, and the 220 will be a standard 500vdc electolytic.
Another question, i want to make a dummy load which i'll use for other builds, can i assume a 10ohm thick film will be fine for this, the electorics store doesnt have 8ohm, unles wirewound which i assume are too inductive.