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Diabolical Artificer · 17th Apr 2021, 8:48 am

Yes,the OPT's is designed for SE operation, came out of a Lowe radiogram driven by an ELL80 which was kaput.

Class AB1 has puzzled me too. When drawing a load line for a PP stage the Class B line is 1/4 of the load,your draw that then the Class A line which is 1/2 the load, then slide the Class A line up a bit until the two lines intersect,that's your bias point. But in a SE stage what load does Class B see? Here on my graph I've assumed 1/2 of the load, not sure that's right. Can't see how you can run a SE stage in Class B without heavy distortion.

With these OPT's I tried a PCL86 first, then tried an ECC88 and 6AQ6A,my reason being the ECL/PLC 86 is designed for amplifying low voltage sources like radio or ceramic PU. In my application the signal source will be an Iphone/MP3, an ECC83 type triode has way too much gain for this ap.

I also tried different OP valves and loads to try and find out why I could only get about 1.5w out this despite different biasing & different loads. Also tried a different OPT, still could only get about 3.5v out before clipping. 3.5^2/5 = 2.45w 3.5^2/8 = 1.5w THD at these levels was over 12%. Figures are approximate.

Looking at my load lines you'll see we get about a 350v V swing, so with a 44:1 T ratio - 350/44 = 7.9v P-P, which is 2.79v RMS. Therefore the limiting factor in all this is the HT & high OPT T ratio, but HT most of all.

I'll have another read of your comments, it'll take awhile to digest em but have include a schematic- valve is PCL86 and load lines. Load line graph is on the Vg2 200v, actual is Vg2 230v but this was too messy to show.

Andy.

17th Apr 2021, 8:48 am	#14
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,670	Re: Single ended Class A OP stages. Yes,the OPT's is designed for SE operation, came out of a Lowe radiogram driven by an ELL80 which was kaput. Class AB1 has puzzled me too. When drawing a load line for a PP stage the Class B line is 1/4 of the load,your draw that then the Class A line which is 1/2 the load, then slide the Class A line up a bit until the two lines intersect,that's your bias point. But in a SE stage what load does Class B see? Here on my graph I've assumed 1/2 of the load, not sure that's right. Can't see how you can run a SE stage in Class B without heavy distortion. With these OPT's I tried a PCL86 first, then tried an ECC88 and 6AQ6A,my reason being the ECL/PLC 86 is designed for amplifying low voltage sources like radio or ceramic PU. In my application the signal source will be an Iphone/MP3, an ECC83 type triode has way too much gain for this ap. I also tried different OP valves and loads to try and find out why I could only get about 1.5w out this despite different biasing & different loads. Also tried a different OPT, still could only get about 3.5v out before clipping. 3.5^2/5 = 2.45w 3.5^2/8 = 1.5w THD at these levels was over 12%. Figures are approximate. Looking at my load lines you'll see we get about a 350v V swing, so with a 44:1 T ratio - 350/44 = 7.9v P-P, which is 2.79v RMS. Therefore the limiting factor in all this is the HT & high OPT T ratio, but HT most of all. I'll have another read of your comments, it'll take awhile to digest em but have include a schematic- valve is PCL86 and load lines. Load line graph is on the Vg2 200v, actual is Vg2 230v but this was too messy to show. Andy. Attached Thumbnails __________________ Curiosity hasn't killed this cat...so far.