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4P10C or 4Π10C tube, any member familiar with?
4P10C or 4Π10C tube, any member familiar with?
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Old 12th September 2019, 04:35 AM   #21
Wavebourn is offline Wavebourn  United States
Anatoliy Lisovskiy
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4P10C or 4Π10C tube, any member familiar with?
I bought sockets exactly made for British Mazda tubes, made in China.

NEW MAZDA style P61 VR66 SP41 SP42 PEN25 OCTAL Ceramic Tube Sockets x10 MO8 BASE | eBay
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Old 14th September 2019, 09:32 PM   #22
smoking-amp is offline smoking-amp  United States
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Here are some traced curves for a Raytheon VT-127
10 mA/div Vert. and 50 V/div Horiz.

a) Pentode 160V on grid 2, 0.8 V steps on grid 1

b) Triode 2 V steps on grid 1

Mu around 12

This Raytheon VT-127 looks just like a 1625 (807) tube except for the MO base and finer grid 1 wire pitch.
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File Type: jpg rsz_vt-127_p_ray.jpg (75.6 KB, 79 views)
File Type: jpg rsz_vt-127_t_ray.jpg (84.7 KB, 70 views)

Last edited by smoking-amp; 14th September 2019 at 09:42 PM.
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Old 14th September 2019, 10:11 PM   #23
Wavebourn is offline Wavebourn  United States
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4P10C or 4Π10C tube, any member familiar with?
Quote:
Originally Posted by smoking-amp View Post
This Raytheon VT-127 looks just like a 1625 (807) tube except for the MO base and finer grid 1 wire pitch.
Grid 2 too; I got red G2 when the amp oscillated without load. And definitely 200V is the maximum that I would supply for G2 of this tube. It is more like vertical video amplifier tube than horizontal sweep one. Like a predecessor for 6P15P, 12HL7, etc.
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Old 14th September 2019, 10:16 PM   #24
6A3sUMMER is offline 6A3sUMMER  United States
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Wavebourn,

Was that oscillation on an amplifier that employed negative resistance?

I worked at a place that used negative resistance on 4 MHz crystal resolution filters for spectrum analyzers (resolution bandwidth filters).
Those were hard to tame.
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Old 14th September 2019, 10:25 PM   #25
Wavebourn is offline Wavebourn  United States
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4P10C or 4Π10C tube, any member familiar with?
Quote:
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Wavebourn,

Was that oscillation on an amplifier that employed negative resistance?
Yes, but not because of it. I just swapped by mistake leads from output transformers to negative feedbacks by voltage of wrong channels, and got a multi-vibrator instead of a stereo amp.

Quote:
I worked at a place that used negative resistance on 4 MHz crystal resolution filters for spectrum analyzers (resolution bandwidth filters).
Those were hard to tame.
Tunnel diodes?

It depends on the value of negative resistance in respect to the impedance of the load. If enough, it flattens frequency response of the speaker servo-damping it; it too much, it oscillates.

I experimented today connecting 8 Ohm speakers to 16 Ohm outputs of a headphone amp through auto-transformer volume control, in last 2 positions speakers start oscillating.

Wavebourn - Headphone amp drivibg 8 Ohm speakers | Facebook
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Old 14th September 2019, 10:35 PM   #26
6A3sUMMER is offline 6A3sUMMER  United States
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The quartz crystals used as series resonators have an intrinsic series resistance.
To narrow the bandwidth, the terminating resistance must be decreased.
That increases the insertion loss of the filter; increases the noise floor of the analyzer because of the required amplification after the filter to make up for the loss.
Negative resistance drove the crystal, and made up for that loss.

Because of the large range of bandwidth settings (and termination resistances), there were some tapped transformers used to make it all work.
. . . Interesting, you used an auto-former on negative resistance amp.

Last edited by 6A3sUMMER; 14th September 2019 at 10:41 PM.
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Old 14th September 2019, 10:42 PM   #27
Wavebourn is offline Wavebourn  United States
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4P10C or 4Π10C tube, any member familiar with?
Quote:
Originally Posted by 6A3sUMMER View Post
Because of the large range of bandwidth settings (and termination resistances), there were some tapped transformers used to make it all work.
. . . Interesting, you used an auto-former on your amp.
Well; I used auto-former before in a parafeed 2 stage hybrid amp with 150V B+, with one tube stage directly driving P-type MOSFET. I postponed that project. It is very promising, but I did not figure out yet how to stabilize better it's working point.
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Old 16th September 2019, 10:55 PM   #28
Wavebourn is offline Wavebourn  United States
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4P10C or 4Π10C tube, any member familiar with?
Judging from anode curves I think that I was wrong assuming that the tube was used for sweep duties in monitors. Most likely, it is a video amplifier tube on steroids.
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