Tube Testing & Curve Tracing

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southboundsuarez
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Re: Tube Testing & Curve Tracing

Post by southboundsuarez »

TriodeLuvr wrote:
Thu 08/12/21 12:48 am
Josh, I'm designing several amplifiers around vintage output transformers that I removed from older commercial gear. The transformers are approximately 3.6K ohms or 3.8K ohms anode-to-anode. The original amplifiers used a tube type that is no longer available, and only the EL34 now matches this impedance well. It's problematic though, because whereas the original tubes were beam power, the EL34 is a true pentode. The screen current requirements of the EL34 are much more challenging, and because these are hi-fi amps, I can't just install a 1K or 1.5K screen resistor and call it a day.

One type of data that's not readily available in any of the EL34 sheets (including the extensive documentation provided by Mullard) is a chart showing anode current as a function of screen voltage. I'd like to see a graph of what happens to anode current with a fixed anode voltage of, say, +400V, a fixed grid voltage of perhaps -26V or -28V, and a screen that's swept from +250V to +400V.

This is something I can do point by point when my current project is off the bench, but that won't have the resolution of a curve tracer. Is this something you're able to do?

Jack
Without getting too off track from OP, I was just curious what orig. tube you were substituting? 8417perhaps?
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Re: Tube Testing & Curve Tracing

Post by TriodeLuvr »

southboundsuarez wrote:
Sat 08/28/21 5:37 pm
Without getting too off track from OP, I was just curious what orig. tube you were substituting? 8417perhaps?
It's the 7355 tube. There have been a number of articles online suggesting the 7591 or various 6L6 variants as subs, but they don't work as well with these low Z transformers.

Interesting what you said about the Hickok; that's the same method I use, except I have a push-pull amp set up for power testing. I bought a large quantity of 6P3S-E a few years back, and I needed to test them four at a time.

We should start a new thread in one of the other forums if you want to discuss any of this. I'd be glad to tell you more about what I'm doing.

Jack
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

If anybody is interested in building one of these tube tester / curve tracers, I have the final parts sets ready. The set comes with the main PCB, an external PSU connection PCB, socket board PCB, and a programmed firmware chip for $135 including shipping within the continental US. Outside of there needs to pay actual shipping. There are two options for the socket boards, one with through-hole devices, and the other one is mostly SMT (only one is included).

Here's a test on my beta unit with the new socket board:
EL84 Beta Unit_plot_1.png

Here's the PCB set (showing two options for the socket boards - only one is included):
FUtracer-PCBs.jpg



Here's my final tester (left), and the beta unit (right):
20211204_164353.jpg

Thanks,
Josh
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

I put the support website up. It's still a work in progress, but the meat and taters are there. Check it out: https://futracer.com

Thanks,
Josh

PS. I wrote it fairly quickly, and didn't do much proofreading, so please let me know if I did something dumb. ;)
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

I had some fun with my laser engraver:
_DSC0152.jpg

It's a little odd that the logos didn't work consistently. Maybe the graphic type, or that it engraved vertically. Or both. Oddly enough, the test subject came out perfectly:
futracer-cover.jpg

Thanks,
Josh
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Re: Tube Testing & Curve Tracing

Post by Bieworm »

Awesome result Josh!!! 🖖
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

We've been working on improving the speed and clarity of the traces, and the results are pretty awesome.
EL34-Tung-Sol-2_plot_1.png
EL34-Tung-Sol-2_plot_2.png
EL34-Tung-Sol-2_plot_3.png
EL34-Tung-Sol-2_plot_4.png

I put up a video of the tracing. You can also now zoom in on the traces and get super detail: https://www.youtube.com/watch?v=OQvVQQVCwgw

Thanks,
Josh
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

I got the new FUtracer v7 boards in, with the PCBA service done...and they're awesome! They did a great job with those tiny little SMT chips.

I built it, calibrated it, and tested it, and it's all good. I'm waiting on a couple tube sockets then I can test the new socket board version that also includes 408A (7pin) and similar tubes.

Once that's all tested, I'll put together some kits for anybody interested.

Thanks,
Josh
FUtracer-v7.jpg
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

The new version 7.0 FUtracer kits are fully tested and ready to go.

This set is 2mm thick, ENIG surface finish, 2u” gold thickness, 2oz outer copper weight, and include the USB chip and socket, PGAs, and anti-static SMT stuff already done. The price for the new kit with the Main PCB, Socket Board PCB, PSU connector PCB, and programmed/user updateable Firmware Chip will be $200. Shipping outside the US is extra, but within the US is included for now.

The new socket board version is mostly SMT. If you want a kit with the SMT work on the socket board done, I will supply the parts and do the SMT work for an extra $50. The pads are all hand-soldering sized, so don't be too scared if you want to do it yourself. ;)

This is the set:
futracer-10-min.jpg

You can contact 'support at futracer dot com' for more info or to purchase a kit.

More information including build and use guides is available at futracer.com.

Here was the final test setup:
FUtracer-v7-final-socket-test.jpg

Thanks,
Josh
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

This came out pretty cool:
futracer-v7.jpg
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Re: Tube Testing & Curve Tracing

Post by Bieworm »

JMPGuitars wrote:
Thu 12/15/22 11:00 am
This came out pretty cool:

futracer-v7.jpg
Dang!!!
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Re: Tube Testing & Curve Tracing

Post by lavrgs »

Bieworm wrote:
Thu 12/15/22 1:26 pm
JMPGuitars wrote:
Thu 12/15/22 11:00 am
This came out pretty cool:

futracer-v7.jpg
Dang!!!
DOUBLE DANG !!!!
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

lavrgs wrote:
Thu 12/15/22 7:05 pm
Bieworm wrote:
Thu 12/15/22 1:26 pm
JMPGuitars wrote:
Thu 12/15/22 11:00 am
This came out pretty cool:

futracer-v7.jpg
Dang!!!
DOUBLE DANG !!!!
Thanks for all your help with the enclosure design!
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Re: Tube Testing & Curve Tracing

Post by Bieworm »

JMPGuitars wrote:
Thu 12/15/22 7:39 pm
lavrgs wrote:
Thu 12/15/22 7:05 pm
Bieworm wrote:
Thu 12/15/22 1:26 pm


Dang!!!
DOUBLE DANG !!!!
Thanks for all your help with the enclosure design!
Too bad you didn't use Papyrus :lol:
very pro device!!!
how do you calibrate it?
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

Bieworm wrote:
Fri 12/16/22 5:26 am
Too bad you didn't use Papyrus :lol:
very pro device!!!
how do you calibrate it?
Papyrus would be on the super special upgrade model. 😉😉

I built a website that details everything from building, to calibration, to basic uses. Here's the calibration wizard tutorial: https://futracer.com/curve-tracer/calib ... on-wizard/

Thanks,
Josh
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Re: Tube Testing & Curve Tracing

Post by roadshow »

Looks real nice.

A few years back I built one of these:
https://www.dos4ever.com/uTracer3/uTracer3_pag0.html

You can find my example build among those posted as built kits.
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

roadshow wrote:
Fri 12/23/22 12:43 pm
Looks real nice.

A few years back I built one of these:
https://www.dos4ever.com/uTracer3/uTracer3_pag0.html

You can find my example build among those posted as built kits.
Me too (3+). My terrible experience between the quality of his hardware/firmware/personality led to the creation of this one. 😉
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Re: Tube Testing & Curve Tracing

Post by roadshow »

JMPGuitars wrote:
Fri 12/23/22 3:04 pm
roadshow wrote:
Fri 12/23/22 12:43 pm
Looks real nice.

A few years back I built one of these:
https://www.dos4ever.com/uTracer3/uTracer3_pag0.html

You can find my example build among those posted as built kits.
Me too (3+). My terrible experience between the quality of his hardware/firmware/personality led to the creation of this one. 😉
Gotcha. Sorry you had issues, I really didn't, but you're way ahead of me. I think I'll take a close look at yours. It looks excellent and very reasonably priced.
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Re: Tube Testing & Curve Tracing

Post by JMPGuitars »

roadshow wrote:
Fri 12/23/22 8:36 pm
Gotcha. Sorry you had issues, I really didn't, but you're way ahead of me. I think I'll take a close look at yours. It looks excellent and very reasonably priced.
I have other people coming from a uT background also, and they LOVE the differences/improvements in this.

Regarding pricing, keep in mind that you need to supply your own parts. There are BOMs on the futracer.com site to help get a good idea of the cost.

I'm also probably going to order some more enclosure sets soon too for people interested in making their own testers, without having to do any metalwork.
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Re: Tube Testing & Curve Tracing

Post by Daviedawg »

Now I understand the source of the name for your unit.

Dd
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