Pumpkin Shunty begins....

[Russellc]

Un matched BC546

These are the small parts that fell off the tape:

 

[Russellc]

I see these BC546 are NPN amplifier transistors. I suppose this rig shown, meant to match N or P Jfets will not work? Is there a similar rig that will?

 

[Zen Mod]

BC parts are bjt , so no JFets

as I said - toss them in circuit in random fashion - no change

or match them on HFe test with your DMM

 

[Russellc]

I'll see instructions with my DMM. If nothing else, I will use as is, hate to not have them with your matching, knowing parts are there, plus I will learn something if nothing else!

I see from google search there is much info, even if instructions are elusive...on with the build.

Russellc

 

[Russellc]

Zenmod, another question on resistors. It concerns Shunty R3, R3a, R6, R6a.
The chart in your cookbook call for 150 ohm to 240 ohms. In the Pumpkin I see a similar deal with R9, R10, R14, R15, R19. what determines the value in Shunty? In Pumpkin? (havent looked at Pumpkin that hard yet, still on shunty)

I am also a little confused with the circuit diagram showing red and green resistors?

thanks,

Russellc

 

[Zen Mod]

those resistor are gate stoppers - to prevent oscillation and develop finer nature of driving demands of mosfets

green and red resistors , last page in CB ?

as written on penultimate page :

 

[Russellc]

Does the range of all these resistors mean "anything" in that range one has on hand, or is there some criteria in value selection? both numbers given and red and greenies? I should have asked question better, it selection of the values that I am asking about.

Thanks again,

Russellc

 

[Zen Mod]

Gate resistors-whatever you have in drawer in said range; green and red ones,value shown

 

[Russellc]

OK, that's good, I am at work now, I will check on red and green ones when I get home.

Russellc

 

[malgre]

shunty progress... xformer connection question

After finishing up some intervening projects, I had time to solder the shunty boards, just need to get the heatsink mounting set (awaiting a few parts needed for that). Still a significant list of things to source, but nice to see some results. I'll probably get a dummy load so that I can test these, I think I'd like to know all is good before the Pumpkin build.

I'd like to double check how to wire transformers - I picked up 4 of the Mercury Magnetics TA-110W from ApexJr, so 2 per shunty. Each one has a 0 - 43V secondary, so to wire 2 together, I would wire the primaries in parallel and the secondaries in series, right?

An externally hosted image should be here but it was not working when we last tested it.

Tod

 

[grimberg]

You should remove the fuses so you can test the first portion of the board.

 

[Zen Mod]

........

I'd like to double check how to wire transformers - I picked up 4 of the Mercury Magnetics TA-110W from ApexJr, so 2 per shunty. Each one has a 0 - 43V secondary, so to wire 2 together, I would wire the primaries in parallel and the secondaries in series, right?
.....

Tod

prior to connecting secndaries to pcb , you must correctly phase them

as you said - primaries in parallel , secondaries in series

measure with Vac meter opposite secondary ends ; if you have double voltage then phase is ok ; if you read almost 0Vac , phase is wrong (in which case just swap leads of one secondary and retest)

when you're sure of phasing , solder to pcb

attached pic made for solo xformer , but same logic applies ...... once when you wire pry. in parallel and connect secondaries in any way , that's practically one system

 

[malgre]

prior to connecting secndaries to pcb , you must correctly phase them

as you said - primaries in parallel , secondaries in series

measure with Vac meter opposite secondary ends ; if you have double voltage then phase is ok ; if you read almost 0Vac , phase is wrong (in which case just swap leads of one secondary and retest)

when you're sure of phasing , solder to pcb

attached pic made for solo xformer , but same logic applies ...... once when you wire pry. in parallel and connect secondaries in any way , that's practically one system

Got it. Thanks for the sanity check, Zen Mod!
Tod

 

[Andrzej Sochon]

Hi!

Many years ago Zen Mod supported me with Pumpkin Shunty PCB's and key-parts.
Now I start to dig at my electronic collection (my wife says: garbage collection) with strong final decision to make Pumpkin Shunty ready. I am retired almost one year and it's perfect time to finalize many things I began before retirement.

Long time no see...I would like to cordially say hello to Mr Nelson Pass and all diyAudio Members, especially Zen Mod 'Choky', James Hill, Peter Daniel and Jacco Vermeulen! Do you remember me?
F-4 still works great.

Best Regards,
Andrzej

 

[Zen Mod]

 

[malgre]

matching mosfets for Pumpkin

Hi Zen Mod -

I'm ordering parts for the Pumpkin boards, and I just realized I'm going to have to match Q5-Q7 (IRF9510) and Q6-Q8 (IRF510). I've never done this before, so a couple of ?s:

- What is a good number of each to buy and test to get the 2 matched pairs needed?
- I've read the Pass article on matching (https://www.passdiy.com/pdf/matching.pdf), so my plan is to use a Shunty as the power supply, but what current am I aiming for? Or is there a better way to go about this?

Any clues appreciated!
Tod

 

[Zen Mod]

if you get them ditto from tube , there is a chance that dozen will give you two decent pairs

completed Shunty is perfect for matching PSU - mosfets need to be matched in range of 30mA

if you need further help , buzz

 

[drpro]

Any stray Shunty/Pumpkin boards looking for a home?

 

[Zen Mod]

you can always get them from Mighty Moi

 

[drpro]

That would be outstanding Mr. Miyagi. Please let me know how much and how you would like payment.
Shipping to Nashville, TN USA
Thanks
David