Thanks, euro21! They are for the grid top cap leads to the 6F5G input tube. With an octal adapter, equivalent 6SF5 could be used as well which do not have a grid cap, so the leads can be removed if they are in use.
And the amp itself. Note that the grid caps leads were meant to be sleeved in paracord, but it did not arrive in time, so just bare cable jacket for now, but have to admit I think it looks good in black.
Well done. Very nice.
I have been thinking a bit about your results and I suspect that most of the distortion you see is coming from the OPT, especially at low-to-medium power.
I have been thinking a bit about your results and I suspect that most of the distortion you see is coming from the OPT, especially at low-to-medium power.
Thanks, gentlemen, I appreciate the input along the way, always indebted to great DIYers whenever a project is finished. This will probably be the last one I do for a long time, it was a doozy...
And duly noted 45. I think the distortion is low enough as to be inaudible or close to it at normal listening volumes. The sound is excellent, great bass definition especially, really enjoying it so far.
And duly noted 45. I think the distortion is low enough as to be inaudible or close to it at normal listening volumes. The sound is excellent, great bass definition especially, really enjoying it so far.
I sleeved the 6F5 grid cap leads with paracord today, gives the amp a little pizzazz.
Here how it looks with some graphite plate RCA 801A.
Here how it looks with some graphite plate RCA 801A.
Graphite plate 801 has a slightly lower internal impedance (there is no indication in the datasheets, but some years ago we have experienced this), so THD would be also slightly lower at moderated power.
I noticed that as well, they run at higher currents at similar grid bias than their non-graphite counterparts. Thanks for the tip!
Here are the gerber files and BOM for the 1mA LND150 CCS I used in this build.
BOM:
Q1 - IXYS IXTP08N100D2 (TO-220)
Q2 - LND150 (TO-92-3)
R1 & R2 - 1K gate stopper (Ohmite OD102JE)
R3 - 1K trimmer (Bourns 3296Y-1-102LF)
C1 - 68pF (Wima FKP2O100681D00JSSD)
RSET - determined by 1K trimmer adjustment with jumper in place.
Highlighted in green on the PCB are the jumper pads, used when adjusting via the 1K trimmer - the jumper can be cut / removed once RSET is in place. RSET of ~300ohm got me a 1mA from the CCS.
Mounting holes are for 3mm screws.
BOM:
Q1 - IXYS IXTP08N100D2 (TO-220)
Q2 - LND150 (TO-92-3)
R1 & R2 - 1K gate stopper (Ohmite OD102JE)
R3 - 1K trimmer (Bourns 3296Y-1-102LF)
C1 - 68pF (Wima FKP2O100681D00JSSD)
RSET - determined by 1K trimmer adjustment with jumper in place.
Highlighted in green on the PCB are the jumper pads, used when adjusting via the 1K trimmer - the jumper can be cut / removed once RSET is in place. RSET of ~300ohm got me a 1mA from the CCS.
Mounting holes are for 3mm screws.
Nice PCB, thanks for sharing. What’s the approximate current range you can set with this CCS?
Regards, Gerrit
Regards, Gerrit
No problem - it's a low-current CCS given the LND150, so around 0-5mA. If running it at the higher end of that range, may need to put a small heat sink on the IXYS FET depending on home much voltage it's dropping.
Here is a higher current version, using a cascode pair of TO-220 FETs. Q1 again can be the IXTP08N100D2 or IXCP10M90S, for Q2 I typically use IXTP08N50D2 or DN2540.
The heat sink is the Ohmite F series, can choose the size based on the sinking need, it's available in 25mm, 38mm, 51mm, and 64mm.
Sink F R | Ohmite Mfg Co
Here is a higher current version, using a cascode pair of TO-220 FETs. Q1 again can be the IXTP08N100D2 or IXCP10M90S, for Q2 I typically use IXTP08N50D2 or DN2540.
The heat sink is the Ohmite F series, can choose the size based on the sinking need, it's available in 25mm, 38mm, 51mm, and 64mm.
Sink F R | Ohmite Mfg Co
DN2540 has TO92 version too (DN2540N3), which has same footprint than LND150.
I regularly use TO92 version FETs as "lower" device in cascode CCS and 1kV IXTP01N100 or 08N100 as "upper", up to about 80mA.
I regularly use TO92 version FETs as "lower" device in cascode CCS and 1kV IXTP01N100 or 08N100 as "upper", up to about 80mA.