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Mono SE84s - "consolidate" transformers?? (Read 1695 times)
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Mono SE84s - "consolidate" transformers??
04/10/12 at 00:09:55
I'm currently putting together 2 zkit1s. Initially I thought I was going to put them in 2 separate boxes and retain the ability of each to run as 2x2W stereo amps, but now I'm pretty sure I just want each to be a 6W mono amp and I may as well put them both into one larger box.
So I'm figuring out layout, dimensions, etc and it dawns on me - instead of having 6 transformers (2 PTs, 4 OTs) is it possible to 'consolidate' down to 1 PT and 2 OTs??
I'm trying to wrap my head around how the transformer specs would 'scale'...the suggested Edcor PT spec is "600V (300-0-300) at 150mA center tapped and 6.3V at 4A"...would the 150mA need to double? Is 4A enough to heat 3 more tubes?
I'm really stumped by how the OT spec would change...again, the sugggested OT is "8kOhm to 6 Ohm"...I have no idea how those values would change ?? Or are the 2 OTs per amp "essential" for bridging into mono and getting 6W output??

I'm not even sure if I'm making sense  :P
Anybody have any suggestions?

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Seasoned Member

pair of dual 18

Posts: 276
Re: Mono SE84s - "consolidate" transformers??
Reply #1 - 04/17/12 at 14:50:54
Hi Matt

I've been waiting for someone else to reply because I don't have tested answers for you...I guess nobody else does either.

You should be able to build two Zkit1's, each in monoblock mode, and use only three transformers.  But I have not done this (yet - are you reading this Chris K?) and I hesitate to throw out answers that might not be 100% correct.

That said, the power transformer should be easy, as there are not that many options available from Edcor.  XPWR137-120 should certainly work, its the same voltages and more than double the current  in both the high voltage and the 6.3 heater voltage.  At $77 its quite a bit cheaper than two of the Zkit1 power transformers at $58 each.  

The output transformers are a bit trickier.  Be sure to use a single Zkit1 per channel, bridging the R and L channels of a single Zkit1 - DO NOT bridge the R channels of two different Zkit1's to get your R channel.  I think you can just parallel the two output tube plate's and drive a single output transformer without any issue, but I'm not 100% sure.  You are going to want either the 5k (GXSE10-6-5k) or the 2.5k (GXSE10-6-2.5k).  My best guess at this time would be the 2.5k but I could be wrong and you really aren't going to know until you try them and look at the results with an oscilloscope, so good luck...you might be better off just buying four of the stock GXSE10-6-8k's, driving each with a single output tube, and then wiring them in series (2 per channel).

Let us know how it goes.

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Steve Deckert

If the 1st watt
sucks why continue?

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Re: Mono SE84s - "consolidate" transformers??
Reply #2 - 02/25/13 at 17:44:11
If you want to run a ZKIT-1 in mono you'll have to leave the design exactly as it is.  Consolidating transformers would change the design from a floating series output stage back to a conventional amplifier where output tubes are in parallel into a single transformer.

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Re: Mono SE84s - "consolidate" transformers??
Reply #3 - 01/09/15 at 15:44:06
When converting a ZKIT1 to mono operation, would it be possible to combine the two inputs (now Y-jumpered together or something similar) down to one gain control potentiometer?
If so, what impedence value changes would I need to modify for input matching?
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