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Search: Posts made by: John L Stewart
Forum: Vacuum Tubes December 10th 16, 03:36 PM
Replies: 41
Views: 3,792
Posted By John L Stewart
Smile -------------------------------------------- Earl...

--------------------------------------------

Early in my career as I interned for my P.Eng I built a regulated DC power supply. 4.5 KV at One amp ain't easy. And one needs lots of safety systems,...
Forum: Vacuum Tubes December 9th 16, 11:29 AM
Replies: 41
Views: 3,792
Posted By John L Stewart
Smile Here Ya Are! Add a couple more KT88s & you...

Here Ya Are! Add a couple more KT88s & you are there.

John L Stewart
Forum: Vacuum Tubes November 8th 16, 08:50 PM
Replies: 6
Views: 1,403
Posted By John L Stewart
Talking [QUOTE=Big Bad Bob;995651]On 11/07/16 06:52,...

[QUOTE=Big Bad Bob;995651]On 11/07/16 06:52, so wittily quipped:
> Build OTL = transistor
> P: 65W
> Vin: 0.775V
> Rin: 400 kő©
> BW: 30Hz - 17kHz
> 0,2%
> CMRR: 70 dB
>
> i...
Forum: Vacuum Tubes October 9th 16, 09:15 AM
Replies: 4
Views: 1,155
Posted By John L Stewart
Smile interesting point, having a set of SE output...

interesting point, having a set of SE output transformers to test output
signals with. "dial-an-impedence" and then let 'er rip. Expensive,
though. I'm looking for low overall...
Forum: Vacuum Tubes February 26th 16, 01:21 AM
Replies: 15
Views: 3,522
Posted By John L Stewart
Smile Patrick is correct, we donít see many audio...

Patrick is correct, we donít see many audio amplifiers making use of the 6U8. However, I did not have to look far to find one. It is one of Patrickís very own early efforts. It has two 6U8s. The...
Forum: Vacuum Tubes February 4th 16, 02:43 PM
Replies: 15
Views: 3,522
Posted By John L Stewart
Smile Biggest problems with pentodes overall is the...

Biggest problems with pentodes overall is the nonlinearity. It's great
for mixer stages, great for frequency synth in radios, great for IF with
AGC, not so good for audio amplification. Basically,...
Forum: Vacuum Tubes February 3rd 16, 04:03 PM
Replies: 2
Views: 1,579
Posted By John L Stewart
Smile very nice, simple circuit. And further support of...

very nice, simple circuit. And further support of my contention that with tube amps, there has been nothing new since perhaps 1970, or so (very probably 1960) but for a few tube variants. We try to...
Forum: Vacuum Tubes February 2nd 16, 10:03 PM
Replies: 15
Views: 3,522
Posted By John L Stewart
Smile Biggest problems with pentodes overall is the...

Biggest problems with pentodes overall is the nonlinearity. .



I'm not a fan of using them in AF circuitry. A dual triode typically
gives you as much open loop amplification using 2 stages,...
Forum: Vacuum Tubes February 2nd 16, 09:50 PM
Replies: 14
Views: 2,334
Posted By John L Stewart
Smile Go back & look at the cct carefully. It is a...

Go back & look at the cct carefully. It is a harmonic generator, meant for guitar or other music instruments effects. Then into the main amp. The harmonics are even order 2nd, 4th, 6th & so on. Not...
Forum: Vacuum Tubes February 2nd 16, 12:37 PM
Replies: 14
Views: 2,334
Posted By John L Stewart
Smile FYI- Doug Hammond already did it for you!! JLS

FYI- Doug Hammond already did it for you!! JLS
Forum: Vacuum Tubes February 2nd 16, 11:37 AM
Replies: 14
Views: 2,334
Posted By John L Stewart
Smile probably - it's something I'd want to do...

probably - it's something I'd want to do [again].

looking for output transformers, ran across THIS one.

https://www.amplifiedparts.com/products/P-T125A

it's a 3W somewhat-universal output...
Forum: Vacuum Tubes February 1st 16, 06:10 PM
Replies: 15
Views: 3,522
Posted By John L Stewart
Smile I would expect screen resistance to change based...

I would expect screen resistance to change based on G-K volts, according
to some kind of general curve, and it's probably NON-linear at that,
based on the actual screen volts, plate volts, plate...
Forum: Vacuum Tubes January 31st 16, 10:54 PM
Replies: 15
Views: 3,522
Posted By John L Stewart
Smile Here are the measurement results with the...

Here are the measurement results with the formatting still intact.

Cheers to all, John L Stewart
Forum: Vacuum Tubes January 31st 16, 09:56 PM
Replies: 15
Views: 3,522
Posted By John L Stewart
Smile Measure Step Size caused by the Screen Bypassing...

Measure Step Size caused by the Screen Bypassing Network
John L Stewart Jan 2016

This paper covers measurements made to determine the frequency response step size caused by the screen bypass...
Forum: Vacuum Tubes January 31st 16, 06:15 PM
Replies: 15
Views: 3,522
Posted By John L Stewart
Smile Measurement of Screen Resistance Example John L...

Measurement of Screen Resistance Example John L Stewart Jan 2016

When designing or building an ordinary vacuum tube audio amplifier with a pentode front end we can for the most part ignore the...
Forum: Vacuum Tubes January 31st 16, 05:26 PM
Replies: 15
Views: 3,522
Posted By John L Stewart
Smile Pentode Screen Resistance (rs) Estimation Example

John L Stewart Jan 2016

In the Heathkit UA-1 12W Amplifier we see a 0.1 microF capacitor bypassing a one Meg resistor supplying the screen current. We might think that we can simply take that RC...
Forum: Vacuum Tubes December 14th 15, 01:57 PM
Replies: 4
Views: 1,669
Posted By John L Stewart
Smile Thanx for your response Peter but it is an air...

Thanx for your response Peter but it is an air cored cross over choke, not a transformer. And the copper band is a right angles to the winding so that coupling would be at a minimum.

We do see...
Forum: Vacuum Tubes December 8th 15, 09:31 AM
Replies: 4
Views: 1,669
Posted By John L Stewart
Smile Copper Band in a Cross-Over Choke??

What measurable benefit might this copper band have? There is what looks like a connexion to go to ground.

Audiophools bad dream or something new?? Anybody got any ideas??

Cheers to all, John L...
Forum: Vacuum Tubes November 27th 15, 07:42 PM
Replies: 6
Views: 1,739
Posted By John L Stewart
Smile Keep on motivating Patrick. I've noticed rigor...

Keep on motivating Patrick. I've noticed rigor mortis sets in early in folks around me who sit back & take it easy. I've never had a 10K km year on the bike but I've done a couple of 8K km & quite a...
Forum: Vacuum Tubes November 23rd 15, 10:33 PM
Replies: 2
Views: 1,579
Posted By John L Stewart
Smile Simple PP Amp with +ve & -ve FB

John Stewart Nov 2015

This circuit is based on an amplifier I built for a friend to be used with a guitar & mike. The date on the schematic is Dec 7, 1958, almost 57 years ago. The entire project...
Forum: About this forum November 18th 15, 05:57 PM
Replies: 1
Views: 11,998
Posted By John L Stewart
Smile Lower it with rope. You might need some pulleys!!

Lower it with rope. You might need some pulleys!!
Forum: Vacuum Tubes July 8th 15, 09:17 AM
Replies: 5
Views: 1,414
Posted By John L Stewart
Smile The e80cc is neither a 12AU7 or 12AX7. See it...

The e80cc is neither a 12AU7 or 12AX7. See it here-

http://frank.pocnet.net/sheets/190/e/E80CC.pdf

& here-

http://frank.pocnet.net/sheets/009/e/E80CC.pdf

It is specíd for digital applications,...
Forum: Vacuum Tubes May 31st 15, 10:38 PM
Replies: 5
Views: 3,106
Posted By John L Stewart
Smile New Projects Iíve added a few more to the group...

New Projects
Iíve added a few more to the group as follows-

Power Frequency Ripple Reduction-

This note describes a simple, low cost power supply improvement. It allows reduction of the power...
Forum: Vacuum Tubes May 18th 15, 02:30 PM
Replies: 5
Views: 3,106
Posted By John L Stewart
Smile OK Paul, on the way to you seperately, John

OK Paul, on the way to you seperately, John
Forum: Vacuum Tubes December 13th 14, 01:30 AM
Replies: 6
Views: 4,009
Posted By John L Stewart
Smile Here is confirmation of Patrick T's comment on...

Here is confirmation of Patrick T's comment on our ability to hear phase. Copied from Fred E Terman's Electronic & Radio Engineering, 4th Edition.
A very good reference text for anyone involved in...
Showing results 1 to 25 of 250

 

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