5k and 8k on Output transformer primary

[zircontweezer]

Hi doing a cathode biased amp. Pair of EL84 power tubes and 5K and 8K primaries on the output transformer. If you have a switch to go from one primary to the other I'm wondering what can happen to the power amp and what would be safe operating conditions. I imagine that the DPDT switch would be brake before make. Doing the switch on a live amp would be dumb? Thanks In advance

[shooter]

would be dumb

I asked the same ? a million yrs ago.
You probably will waste a switch and time finding there ain't much perceived difference.
IF you do use a switch, put it in back, switch it powered off.
the better option, build it, leave wires long, play at 5k for a day or two, re-wire, repeat, find your happy wire

[pdf64]

It’s certainly can cause problems to switch current in highly inductive circuits.
There again, if the goal is to generate sparks, it’s just the ticket

[sluckey]

I don't recall seeing any EL84 amps using a 5K OT. I'd just heat shrink the 5K leads and tuck out of the way.

[jordan86]

Trinity Amps has a TC15 amp kit that has these exact options on their OT. They call them the “Matchless” and “Vox” settings. I’ve built one and was surprised at the difference I heard. Maybe it’s their iron but the differences were more apparent than I expected them to be.

You can find their schematic, layout, and builders guide here. The builders guide is very detailed and I imagine there is a whole page committed to the OT wiring.
https://www.trinityamps.com/support/

Edit: check page 40/41 of the builders guide. Not sure what his switch is rated for. Layout file says DPDT 5A.

[sluckey]

Learned something new. I never knew the Lightning used a 5K OT. I built one several years ago and never bonded with it. I used an 8K OT. Wonder if that's why I never liked the amp?

[jordan86]

I know I’m just the lowly messenger here but it sure seems like a good day when the Sluckey himself says he “learned something new” from your post. If it weren’t so early I’d crack open a cold one as I pat myself on the back.

[jordan86]

With the TC15....The 5K to me was noticeably louder and cleaner. The 8K was grittier and less volume. Both good fir different things.

[sluckey]

I built my Lightning back in '09. At the time I was looking at everything "Lightning" including the TC15. Trinity already had his 5K/8K switch at that time but I had forgotten about it or just never noticed. Probably because my donor OT only had 8K primary. Anyhow, thanks for teaching me. It's that old dog thang!   

[kagliostro]

Many thanks for sharing this info

I never know before about 5k load

on a pair of El84 tubes

This Is very interesting to me

Franco

[sluckey]

Hi doing a cathode biased amp. Pair of EL84 power tubes and 5K and 8K primaries on the output transformer.

Which OT? Where did you get it? I'm tempted to try this in my dual lite amp.

[PRR]

What is the difference 8K vs 5k, or putting 8r on the 16r tap?

Yeah, it's not 5:8 but 4:8 is near. And with a 4-8-16 winding, super quick to try.

[pdf64]

I seem to remember reading that one of the USA Vox based boutique builders used the same OT for both their 4xEL84 and 2xEL84 models.

[2deaf]

What is the difference 8K vs 5k, or putting 8r on the 16r tap?

Putting an 8r load on the 16r tap has a much more dramatic effect on the power amp open loop gain than switching from an 8K tap to a 5K tap.  The difference between the two scenarios with regard to gain reduction from NFB may be a significant factor in the way each one sounds. 

[PRR]

...Putting an 8r load on the 16r tap has a much more dramatic effect on the power amp open loop gain than switching from an 8K tap to a 5K tap.  The difference between the two scenarios with regard to gain reduction from NFB may be a significant factor in the way each one sounds.

8-on-16 should be equivalent to a 4Kct loading. Which is 80% of a 5kct loading. Not a lot of difference. Tubes vary 20%, and speakers are all over the place, yet the flavor is similar?

Does the Matchless Lightning used NFB? (I'm no expert.)

[sluckey]

Lightning does not use NFB. We may have drifted a bit from the OP. First popped up TC15, then Lightning. Who knows what the OP has.

[jordan86]

Trinity sells this transformer, custom made by Heyboer. You can order it directly from them. Not sure if that is what the OP has.

[2deaf]

...Putting an 8r load on the 16r tap has a much more dramatic effect on the power amp open loop gain than switching from an 8K tap to a 5K tap.  The difference between the two scenarios with regard to gain reduction from NFB may be a significant factor in the way each one sounds.

8-on-16 should be equivalent to a 4Kct loading. Which is 80% of a 5kct loading. Not a lot of difference. Tubes vary 20%, and speakers are all over the place, yet the flavor is similar?

Does the Matchless Lightning used NFB? (I'm no expert.)

I was telling my girlfriend a number of months ago (although it could have been years because it seems the same to me lately) that PRR quotes people in two different ways.  When he quotes people the way he usually does, it's good ole PRR.  But when he quotes people the way that I do and the way that he did here, the response seems to have a flavor of mashed potatoes with a side of apples and oranges.  So much so that I really don't think that PRR wrote this.  Maybe his snotty-nosed little b@st@rd nephew gets on his computer when he forgets to sign out.  Now, I carefully worded what I said just in case pdf64 might get on me.  I didn't say that any amp in particular had NFB, just that the gain reduction from NFB is affected differently in the two scenarios.  Although the primary impedance changes with a speaker mismatch, the turns ratio to the NFB tap doesn't.  The change in primary impedance has a potent effect on the power tube gain while the gain of the OT for NFB remains constant.  When the primary tap is changed from 8K to 5K, the turns ratio to the NFB tap changes in addition to the power tube gain and the two gains partially cancel out.  This is why a speaker mismatch has a bigger effect on power amp open loop gain than changing primary taps. I don't know off the top of my head if the Matchless Lightning had NFB, but I'm confident that they were pretty much matched at every turn.   

[zircontweezer]

Yes Jordan has worked out my tentative question I've had the iron for quite a while and I'm doing a Trinity TC-15 or Matchless HC-15 and I'm just ignorant of what the Trinity /Heyboer dual primaries will do tone wise and safe practice wise. Thanks for the information Jordan sounds promising. I'm not quite sure of the theory side of what the amp does switching between the two but guessing the curve of the knee? changes .

[zircontweezer]

With the TC15....The 5K to me was noticeably louder and cleaner. The 8K was grittier and less volume. Both good fir different things.

Ok I did assume the 8k was Vox territory and cleaner but happy to be educated and hopefully it will be finished in a month or so to hear the difference. The Trinity design has 8k as "Munch" and 5k as "crunch" which seems a bit vague and the build info didn't state exactly what to expect.

[shooter]

Trinity design has 8k as "Munch" and 5k as "crunch"

in Engineering that's called marketing 

[zircontweezer]

Had the amp built for a while now. Still waiting on the head shell as it's getting built by someone with better wood working skills and tools. I've just measured the output with 1khz signal and 8 ohm dummy load. My Cro gave me clean output on the 8k (Munch) at 9 watts and max output 14 watts. With the 5k (Crunch) primary I got 2.5 watts clean and max volume 5 watts!. So a big difference on paper but I haven't really had much of a play with it at stage volumes to notice, I'm glad it's got a Master as I'm just practicing at home and it sounds very loud both sides, I did just A/B with same settings on guitar and amp and it is noticeable. It is interesting that Jordan had the reverse opinion of which side was louder but I've double checked the wiring and layout documents on mine. Shall start a build thread when I get my head shell.