Hi Tim ,
Thanks . I have looked at one or two of the PC sound card apps on line , but not sure what is best to try at this stage. Time of coarse is another factor. I can look more at this now we are in holiday mode.
I just did some capacitance readings with my Avo LCR meter. All secondary windings shorted together on one short test lead and the other test lead on one end of the half primary gave me 3.7 nF between them. The two half prims CT ends connected as they would be I get double the 3.7 nF One end of half primary to the lam. core gave 400 pF. Another bobbin the same size, that's 51 mm x 64 mm x 71 with two ordinary windings on it, gives 2 nF between the prim and sec windings. With the Williamson transformer there is 8 effective capacitor plates made up of prim and sec interleaved and the screen grid tertiary windings interleaved in there as well (only .15 mm wire) x the two half's which is 16 all up. So it makes it hard to get the capacitance down lower. Anyway the OP t's do work and amp sound good. I was looking at breaking up the windings from 2 sections into 4 or 8 across the bobbin to try and reduce interwinding capacitance. That would be fun to wind. Leakage inductance on whole primary winding with secondary shorted gives 14 mH. The whole prim with sec open reads 110 H. Of coarse it is the phase response giving me difficulty at the high freq end but on present amp I have overcome it . It rolls off by around 3 db at around 20 Khz . My ears can only hear to around 15 Khz now so that's not an issue for me. I will let you know how the second amp works out .
I see the EL36 has a low anode resistance spec and only 12 watts max anode dissipation. Designed for efficient switching. I would like to try say 2 parallel of those aside in PP Class AB UL and use a much lower DC HT voltage. That would help mitigate OPT winding capacitance issues . Prim windings can be arranged for much lower impedance. Anyway I don't have any of those valves . I did my apprenticeship when colour TV in NZ was already in full swing . We serviced a few valve black and white sets at that time in the early 1980's. Now here I am again this time playing with valves again. I stopped over once in Niue on the way to the Cook Is. Now I generate megawatts of power from diesel, solar and wind here in Tonga with the local power company.
Happy new year anyway.
Regards
Murray.
Thanks . I have looked at one or two of the PC sound card apps on line , but not sure what is best to try at this stage. Time of coarse is another factor. I can look more at this now we are in holiday mode.
I just did some capacitance readings with my Avo LCR meter. All secondary windings shorted together on one short test lead and the other test lead on one end of the half primary gave me 3.7 nF between them. The two half prims CT ends connected as they would be I get double the 3.7 nF One end of half primary to the lam. core gave 400 pF. Another bobbin the same size, that's 51 mm x 64 mm x 71 with two ordinary windings on it, gives 2 nF between the prim and sec windings. With the Williamson transformer there is 8 effective capacitor plates made up of prim and sec interleaved and the screen grid tertiary windings interleaved in there as well (only .15 mm wire) x the two half's which is 16 all up. So it makes it hard to get the capacitance down lower. Anyway the OP t's do work and amp sound good. I was looking at breaking up the windings from 2 sections into 4 or 8 across the bobbin to try and reduce interwinding capacitance. That would be fun to wind. Leakage inductance on whole primary winding with secondary shorted gives 14 mH. The whole prim with sec open reads 110 H. Of coarse it is the phase response giving me difficulty at the high freq end but on present amp I have overcome it . It rolls off by around 3 db at around 20 Khz . My ears can only hear to around 15 Khz now so that's not an issue for me. I will let you know how the second amp works out .
I see the EL36 has a low anode resistance spec and only 12 watts max anode dissipation. Designed for efficient switching. I would like to try say 2 parallel of those aside in PP Class AB UL and use a much lower DC HT voltage. That would help mitigate OPT winding capacitance issues . Prim windings can be arranged for much lower impedance. Anyway I don't have any of those valves . I did my apprenticeship when colour TV in NZ was already in full swing . We serviced a few valve black and white sets at that time in the early 1980's. Now here I am again this time playing with valves again. I stopped over once in Niue on the way to the Cook Is. Now I generate megawatts of power from diesel, solar and wind here in Tonga with the local power company.
Happy new year anyway.
Regards
Murray.
Hi Murray, apart from using an LCR meter, I've made capacitance measurements of a half-primary shunt capacitance using an RC filter roll-off technique (as per page 6 of link below). Normally the prim CT, and a sec tap, and the core get connected together, as per an operating amp. The primary inductance varies a lot with applied voltage, and 5 to 20Vrms of mains frequency excitation have been the typical benchmark levels used.
The output tube plate resistance comes in to play for the low frequency stability - some design details are in link. I've seen an estimate of 450 ohm for EL36 triode mode, which is about a third that of a KT66 in triode mode, and about a quarter of an 807.
https://www.dalmura.com.au/static/Williamson%20design%20info.pdf
Ciao, Tim
The output tube plate resistance comes in to play for the low frequency stability - some design details are in link. I've seen an estimate of 450 ohm for EL36 triode mode, which is about a third that of a KT66 in triode mode, and about a quarter of an 807.
https://www.dalmura.com.au/static/Williamson%20design%20info.pdf
Ciao, Tim
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