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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
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Old 8th July 2019, 08:07 PM   #31
pcan is offline pcan  Italy
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
The Zenith Royal 2000 is one of the first portable transistor radios with FM; could be the first one that was built in the United States. Previous portable transistor radios, with the exception of at least one Sony model and a European product (B&O), were AM only. Nevertheless, it is a milestone and deserves a spotlight on a radio collection. Useful informations for Zenith radio collectors are on the book "Zenith Transistor Radios - Evolution of a Classic" ISBN 0-7643-0015-6
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Old 8th July 2019, 11:03 PM   #32
wiseoldtech is offline wiseoldtech  United States
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Quote:
Originally Posted by craigtone View Post
I got my info here: 1959 Zenith Royal 2000 - 1958 Thunderbird advertisement

Pretentious much?

Of course you got your info from an internet source, I already knew that, and know about several internet "advertisements", dated 1961-1965.
And dates and details can be easily "photoshopped' to look authentic, I've done it myself for laughs.



However, I also know that Zenith stole the idea and some of the design from a 1958 Sony Am/Fm portable.
Yes, perhaps, the Royal 2000 was "made" in the USA, but with no mention of Sony, of course.
Aggressive marketing, leaving out certain details is the norm.



I got "my" information straight from a Zenith executive back in the 1970's when our repair shop was invited to participate in a Zenith dealer symposium related to their new Chromacolor TV's.

Last edited by wiseoldtech; 8th July 2019 at 11:05 PM.
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Old 11th July 2019, 11:08 PM   #33
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
Ok.

So I added that gain stage. I would have used a 9 pin tube, but I didn't have any sockets so octal it is.

Also added an STR75/60 VR tube to drop -110V to -78V. This makes the amp make sound sooner. It was taking 2m30s to bias up but now it's only 45 seconds.

Of course, this meant changing a 390V module for a 280V module into a voltage doubler for 560V. Changing the 12V supply to deal with the extra inrush, and adding a 150R resistance in series with the AC supply from the 560V doubler as well.

Still, after ironing out a few issues (I used 27k instead of 2k7 for the cathode of the driver, oops!) it's pretty amazing if I say so myself.

I've also increased the bias in an attempt to chase out some distortion the sounded like blocking/clipping, but that wasn't the problem. It was a bad tube, but I was too lazy to lower the bias point.

So now the OP is 320V plate, 0.4V cathode, 40mA current for a Pd of 12.8W per 6P43P.

The 6N8S is running 310V plate @ 4.5mA per section.

Of course, I'm using DC boards for the VAPIDRIVE and bias... I even annotated a picture

Oh, and the heaters are untwisted AC but since it's a power amp there is still no hum. The PT for the heaters is 12.6VCT. I grounded the CT and use one half of the transformer for each channel. Chassis ground return for everything, but I ground the power supplies to the same point. I wanted to see just how sloppy one could get without it being detrimental. As long as I can put my ear to the cone of the speaker and not hear hum, I'm good.

My Canadian friends might recognize the "lucky coin" from the Mandarin (Canadian Chinese buffet restaurant).

Also, the relay only brings in B+ for the output tubes if the supply for the bias supply is working. When I get a 120V relay, it'll be connected to the actual bias instead of the supply.
Thoughts?
Attached Images
File Type: jpg 2019-07-11 16-01-01-annotated.jpg (1.07 MB, 152 views)
File Type: jpg 2019-07-11 18-04-14.jpg (619.5 KB, 150 views)

Last edited by kodabmx; 11th July 2019 at 11:15 PM.
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Old 11th July 2019, 11:54 PM   #34
kodabmx is offline kodabmx  Canada
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
Default Schematic

Here's the current schematic minus the power supply.
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Old 12th July 2019, 02:28 AM   #35
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
Forgot to mention. 1V in == 11V out now...
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Old 16th July 2019, 04:29 PM   #36
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
A sky shot of the finalized amp. Along with a gratuitous rack shot.
Yes, I know I should dust more...
Attached Images
File Type: jpg 2019-07-16 12-15-13.jpg (715.0 KB, 98 views)
File Type: jpg 2019-07-16 12-31-14-crop.jpg (276.5 KB, 90 views)

Last edited by kodabmx; 16th July 2019 at 04:37 PM.
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Old 16th July 2019, 04:44 PM   #37
dhaen is offline dhaen  Europe
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Great! You must be single...
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Old 16th July 2019, 05:09 PM   #38
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
Nope... I just have a very awesome lover and no kids... The entire place is only 380 sq ft. 35m3... I'm a pretty fortunate guy really now that you bring my attention to it
And if anyone has a lead on the missing knob for the EQ, please let me know
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Old 16th July 2019, 05:47 PM   #39
dhaen is offline dhaen  Europe
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Quote:
Originally Posted by kodabmx View Post
Nope... I just have a very awesome lover and no kids... ...
Even better, enjoy it while it lasts....
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Old 4th August 2019, 10:06 PM   #40
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
An update: This is the final schematic and a snap of the amp. All recycled parts, and the performance is excellent. I will measure the power output properly soon, but I can tell you it's at least 20W... All from triode connected tv tubes! The secret lies in the fact they support a high peak current, allowing a 3k plate to plate load. The 1Vin == 11VOut is taken with a 6R load == 20W.

The middle tube is an SR75 used for the -bias supply. As usual, I'm using AB-4 from Audioamp.eu because I had it from a previous project, and it works well. The 530V supply is derived from a DC-AC boost converter (delon doubler from 280V) running from a 12V SMPS, so it the -110V bias from another DC-DC converter which is filtered and dropped by the SR75. The heater supply is AC and as an experiment, I ran it untwisted, single feed with chassis return. No hum. The left channel runs of one half, the right off of the other, transformer is center tapped to chassis. I figured if there was any hum, I could easily convert it to DC. The relay is controlled by the 12V SMPS and connects B+. I figure this was if there is a bias failure, the B+ won't energize either.

Thanks to this community. Without your help over the years, this wouldn't have been possible.
Attached Images
File Type: png 6F12P-6P43-PP-Triode (2).svg.png (230.6 KB, 26 views)
File Type: jpg 2019-08-04 18-21-08.jpg (641.9 KB, 21 views)
File Type: jpg 2019-07-11 14-17-24.jpg (1.07 MB, 14 views)

Last edited by kodabmx; 4th August 2019 at 10:31 PM. Reason: Typo
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