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Simple Question: Is this device in Pentode or Triode mode??
Simple Question: Is this device in Pentode or Triode mode??
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Old 10th July 2018, 11:45 PM   #1
veronicasmithen03 is offline veronicasmithen03
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Join Date: Jun 2018
Question Simple Question: Is this device in Pentode or Triode mode??

Hey all, this is my second attempt posting this (lost my first post!).

I bought an FX-Audio Tube-01 Preamp/buffer (it does provide gain) and want to use it with the Yugoslavia 6HM5 tubes like the Little Dot users do. I came across a post from someone saying NOT to use this tube in a different ef95/6ak5 amp unless the amp has the tubes strapped as a triode. So that's what I'm trying to find out: is this device wired for triode or pentode mode? It is a really low power device (12v) so I'm not entirely sure there is enough juice to run it as a pentode?? (I'm brand new to tubes, and learning as I go).


Here are some pictures of the board, and a "schematic" I was told by several users should be pretty darn close (looks like most of the cheap chinese 6j1 preamp/buffers are fairly similar). All I need to know is if it is setup as triode, or pentode mode.


Code:
https://www.ebay.com/itm/FX-AUDIO-TUBE-01-DC12V-Preamplifier-Tube-Amplifier-Buffer-6J1-HIFI-stereo-audio/263472607905?
Code:
https://www.circuitlab.com/circuit/9vnehk/fever-6j1-tube-pre-amp-circuit/


If none of that is helpful, I can remove the PCB and take some pictures of the traces on the front/rear of the PCB.

Thank you very much, and my apologies regarding my noobness!
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Old 11th July 2018, 12:02 AM   #2
gingertube is offline gingertube  Australia
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The circuitlab schematic shows anode and Grid 2 strapped together - so triode mode.
The power supply generates +24V and -24V so the tube is running from an effective 48V supply.
I would ONLY contemplate running pentode mode if you need more gain.

Cheers,
Ian
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Old 11th July 2018, 03:47 AM   #3
PRR is offline PRR  United States
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This is not a "simple question".

You have an ebay link to a low-low price product with no documentation.

You have a link to a schematic which "may" be related. But no sure proof.

The ebay images seem to show a voltage converter. The 12V you put in may be jacked-up to +/-24V or 250V... we can't be sure from the pictures.

There is the question of if the tube you want to use has the same pin connections as the tube the product is designed to use.

The "simple answer" is to stay with what it was designed for. Tubes is tubes, there's not really huge differences between them. Yes, people with highly refined systems can detect small differences and rave about them.

The bold answer is to stick it and see. It's only $32 plus the tube. I've risked more with less justification.
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Old 11th July 2018, 05:07 AM   #4
Aridace is offline Aridace  Panama
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What you could do in case it doesn't work well enough, is to modify the circuit to an ultra linear variant (both AC and DC to screen grid halved) - below 0.05% THD (mostly 2nd) at thrice the output listed on eBay. Works for most pentodes, not just the modeled SV83, with lower distortion and higher gain than in triode mode .
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Old 11th July 2018, 07:10 AM   #5
Alllensoncanon is offline Alllensoncanon  United States
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Simple Question: Is this device in Pentode or Triode mode??
Quote:
Originally Posted by veronicasmithen03 View Post


#1 Is this device wired for triode or pentode mode?



#2 It is a really low power device (12v) so I'm not entirely sure there is enough juice to run it as a pentode?.


#1 It is connected as Triode. Pin 6 of 6HM5 is internal shield. If you replace the 6J1 with it, the shield will be connected to plate. It is properly not a good idea. Shield typically should be grounded.


#2 It has +- voltage doubler built-in. Effectively the plate should see 60V or so. It is still half of the reference circuit from the 6HM5 data sheet. This is a major limitation for this low cost product.
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Old 11th July 2018, 07:30 AM   #6
veronicasmithen03 is offline veronicasmithen03
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Quote:
Originally Posted by Alllensoncanon View Post
#2 It has +- voltage doubler built-in. Effectively the plate should see 60V or so. It is still half of the reference circuit from the 6HM5 data sheet. This is a major limitation for this low cost product.
I'm pretty sure the schematic is for a slightly different device. I'm pretty certain mine has a voltage trippler which still doesn't get me up to 100% but I have some variable voltage low ripple SMPS that I should be able to dial up a bit past 12v without blowing the default caps. Might give that a try if it isn't @ all satisfactory! But I will keep that in mind, thank you very much for you advise and for answering my question!

As for the pin #6, I'll have to look into how the LD MK2 goes about dealing with this pin when set in EF95 mode. I know its a common tube to use in that mode with no mods so I'll take a look at the circuit and do some more research into that before proceeding. Thanks for pointing that out!



Quote:
Originally Posted by Aridace View Post
What you could do in case it doesn't work well enough, is to modify the circuit to an ultra linear variant (both AC and DC to screen grid halved) - below 0.05% THD (mostly 2nd) at thrice the output listed on eBay. Works for most pentodes, not just the modeled SV83, with lower distortion and higher gain than in triode mode .
Hey thanks for that! That is really interesting and I appreciate the schematics as well. I will keep that in mind!



Quote:
Originally Posted by gingertube View Post
The circuitlab schematic shows anode and Grid 2 strapped together - so triode mode.
The power supply generates +24V and -24V so the tube is running from an effective 48V supply.
I would ONLY contemplate running pentode mode if you need more gain.
Thank you very much for answering my question! I appreciate it very much.



Thanks everyone for your kind and technical responses. I very much appreciate it.

Last edited by veronicasmithen03; 11th July 2018 at 07:47 AM. Reason: Had to respond to other users
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Old 11th July 2018, 04:28 PM   #7
Aridace is offline Aridace  Panama
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Quote: Hey thanks for that! That is really interesting and I appreciate the schematics as well. I will keep that in mind!

My pleasure. I was modeling circuits for the most linear driver and was quite amazed that it performs so well: at 300V supply voltage (and the emitter resistors changed to 3k3 each) it can deliver over 80V(pp) at THD (only 2nd and 3rd) of just 0.026 %. So a batch of SV83s has been ordered after checking it was real.
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