Search found 641 matches

by little eddy
Wed Nov 13, 2019 4:40 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

So a bit of tinkering and the inverse RIAA is sort of working. Initially there was a bit of 'undershoot so have reduced the series RIAA resistor from the theoretical 284k to 269k, resulting in: Inverse RIAA 269k small.jpg My question is how much more can this be improved, is this reasonable, and I g...
by little eddy
Tue Nov 12, 2019 2:44 pm
Forum: Valves
Topic: Valve Tester
Replies: 2
Views: 153

Re: Valve Tester

Am I right in assuming you test the valve with 2 different bias conditions and then calculate gm by (Ia1-Ia2)/(Vg1-Vg2)?
by little eddy
Mon Nov 11, 2019 4:12 pm
Forum: Valves
Topic: Valve Tester
Replies: 2
Views: 153

Valve Tester

Has anyone made one that could be used to measure/calculate gm and Ia?

What about the attached? https://www.valveheaven.com/wp-content/ ... tester.pdf
by little eddy
Mon Nov 11, 2019 4:07 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

So getting psyched up for trying to do a square wave test. Trying out my cheap Chinese signal generator and oscilloscope. Is the attached image showing a good enough waveform to do this test, shown at 950Hz? Square Wave Small (2).jpg The Inverse RIAA card has a selector switch for -40 and -60dB, so ...
by little eddy
Sun Nov 10, 2019 1:37 am
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

I'm inclined to remove them if not fully justified in my quest for simplification.

As per the original amplifier stage design, although perhaps well intended, they seem excessive and less may hopefully be more!
by little eddy
Sat Nov 09, 2019 5:35 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

Why might the designer have added the 100k and 220k resistors to the cathodes of the bottom and top triodes in the regulator?

Looking at my Rozenblit book, with a single triode regulator, there is no resistor from the ECC83 cathode to the regulated output.
by little eddy
Sat Nov 09, 2019 4:43 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

Well spotted Mike. I couldn't understand why the EL84 Vg was so large when looking at it's triode characteristics, should have been a volt of so at the most for Va 100V and 35mA. Left the load at 470k (as per a Rozenblit circuit) and I think all is OK now with voltages as attachment :D . 41V across ...
by little eddy
Fri Nov 08, 2019 6:17 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

Will do. From what Nick said about my proposed pentode design, the load resistor should come off the anode side of the EL84 anyway, so probably an improvement over the originators design. Just a bugger to do. Running short term with the pre-amp ECC82s removed to limit the load. Sounds great this aft...
by little eddy
Thu Nov 07, 2019 6:46 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

By g2 on the el84 I assume you mean g1 on pin2? Yes your assumption is correct. The voltage on the lower triode anode is fixed by the upper cathode voltage which is set by the voltage on its grid. The upper triode grid voltage remains fixed at around 134V, as per the voltage divider on the output, ...
by little eddy
Thu Nov 07, 2019 1:40 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

So testing the cascode, as I increase the load current from 9 to 24mA, the only measurements that really alters is Vg2 of the EL84 and Va of the top 6N2P (tied together by the 1k5 grid stopper). They start at 187 and gradually fall to 170V. Vk of the 6N2P is steady at 137V up to then so all OK with ...
by little eddy
Thu Nov 07, 2019 12:52 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

Thanks Nick.

When I look at the MJ design, he has the EF86 g2 at 20V for Zener/Vk/Vg3 of 85V. Seems awfully low - is this correct? Assuming it is, I will target 26V, similarly 65V below the Zener voltage.

In terms of the EL84 g2, 220R/1W seems to be about the average?

Mike.
by little eddy
Thu Nov 07, 2019 10:12 am
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

I was going to post last night but thought I'd investigate the current design further, even if it is just for me learning a bit more. Coincidentally I had been looking at an EF86 pentode regulator in MJ. I had drafted the attached, but inevitably have the following questions: Yes I can with a bit of...
by little eddy
Wed Nov 06, 2019 11:27 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

I'm going to make a series of measurements so I can better understand how the regulator valve conditions are affected as I increase the load current at 225V output. Is that the 'load' at 470k larger than would be expected and is this 'compressing' the voltage remaining for the two triodes. Update to...
by little eddy
Wed Nov 06, 2019 3:39 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

Nick. Did some testing with the full valve complement drawing around 30m, voltages as attached. Very strange the high voltage between the two 6N2P triodes. So as you suggested, tried on no-load (fine), and then gradually added valves. The regulator seemed to work fine @ 225V up to around 24mA, but t...
by little eddy
Tue Nov 05, 2019 3:58 pm
Forum: Everyones Projects
Topic: Snail Phono Pre
Replies: 223
Views: 46967

Re: Snail Phono Pre

Sorry but I need some help with the series regulator I inherited from the original builder as attached. To allow me to increase the valve operating points, I need to find an additional 15V. I had thought the output voltage was determined by the Zener, and 3 way voltage divider so Vout would be 91/11...