Hi Pieter,
I agree with you, there is too much focus on isolated parameters.
Your statement about DCR is interesting. I would understand why a low DCR is beneficial in a transformer. But could you explain why a low DCR would also be beneficial in a plate choke? Just curious, I have not done comparisons in different DCR plate chokes so have no opinion on this yet.
Best regards
Thomas
I agree with you, there is too much focus on isolated parameters.
Your statement about DCR is interesting. I would understand why a low DCR is beneficial in a transformer. But could you explain why a low DCR would also be beneficial in a plate choke? Just curious, I have not done comparisons in different DCR plate chokes so have no opinion on this yet.
Best regards
Thomas
Sorry, but it was not meant to be agressive.
Let me say it in other words: over the years I have extensively tried different winding techniques to maximize HF bandwidth with high Rp tubes and step-up or step-down ratios, because that is the most difficult area for winders, a major challenge so to say.
Based on experience I know what is about possible, and minus 3 dB with a 7k tube.....forget it. Even for a 300B (700 ohms or so Rp) output transformer this would be a really good spec when also the full low frequency power bandwidth would be there.
It seems to make more sense if you would indicate what you would expect (or require) from this type of interstage transformer. A good winder should say if these requirements could be met.
Let me say it in other words: over the years I have extensively tried different winding techniques to maximize HF bandwidth with high Rp tubes and step-up or step-down ratios, because that is the most difficult area for winders, a major challenge so to say.
Based on experience I know what is about possible, and minus 3 dB with a 7k tube.....forget it. Even for a 300B (700 ohms or so Rp) output transformer this would be a really good spec when also the full low frequency power bandwidth would be there.
It seems to make more sense if you would indicate what you would expect (or require) from this type of interstage transformer. A good winder should say if these requirements could be met.
Hi Thomas,
For output transformers low DCR's are clearly of advantage (damping / output impedance) because of the low impedance loudspeaker interface.
For interstage transformers and anode chokes this should not be of equal importance because loads are generally high impedance.
Nevertheless in my experience the lower DCR types just sound better, "easier" on the ear. Then one is tempted to search for reasons, and when searching, you want to find something "important" without knowing or able to prove wether it really matters. This forum's ever ongoing thread "John Curl's blowtorch amplifier" with "deep going" discussions on resistance induced noise and eddy currents is a nice exemple of that IMHO.
Maybe one of your points, headroom, is also playing some beneficial role here.
Be sure that what has happened in Japan, and what is still going on there, is of major concern for all of us!
I'm the one using the HA-133, and it's my optimal solution. (Because it's what I've got, but there is no question it is an excellent transformer.) Rated at 30Hz - 40kHz (not sure of dB window) in this application it is good from a little below 30Hz to about 20kHz and is actually pretty flat - way better than -1dB over this range with the 26. Total primary DCR for both windings in series is in the region of 600 ohms.. Split primaries, and multi-tapped split secondaries with a permalloy core. Rated 8mA DC on the primary, I've found it works best at up to 6mA - recollect some odd behavior when run at 8mA. (I've been running this pair for about 10yrs now.)
Here's a good resource for owners of UTC transformers: UTC Data Includes specifications, and connection diagrams for many different types..
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Hi Kevin,
Checking HA-133 specs I see that primary impedance is indicated being "15k".
We know that transformers in general have no "impedance", but impedance ratios, however I prefer "winding" ratios.
All one can say is that a "15k" primary impedance asks for a minimum value of primary inductance. Though the absolute value measured by some inductance bridge does not tell us everything it gives an indication, and I would say that the HA-133 should have at least 150H. It is a pity that UTC did not give specs of primary L.
Did you ever measured it?
Checking HA-133 specs I see that primary impedance is indicated being "15k".
We know that transformers in general have no "impedance", but impedance ratios, however I prefer "winding" ratios.
All one can say is that a "15k" primary impedance asks for a minimum value of primary inductance. Though the absolute value measured by some inductance bridge does not tell us everything it gives an indication, and I would say that the HA-133 should have at least 150H. It is a pity that UTC did not give specs of primary L.
Did you ever measured it?
Unfortunately I have no means of accurately measuring it, but my one attempt long ago did indicate that it had a higher primary inductance than I could measure at the time which was 100H..(I've heard technically unsubstantiated comments to the effect that it is in the >170H range.) The winding ratio is ~ 5:1 which obviously depends on the taps chosen on the secondary side, but for the 500/600 ohm taps that's the ratio. I'm not sure why it didn't occur to me at the time to measure the inductance of one half of the primary as that should have been well within the range of the meter I was using, (at 1/4 of the total inductance) but I didn't. (The only working meter I have now is good for only 20H, and the bridge which can do 200H is not in working order, and probably won't ever be.)
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Hi Dave,
In theory by measuring secondary inductance you can calculate primary inductance, sure (1H of measured secondary L should be 25H primary L in case of 5:1).
In practice however it does not apply very accurately; I often check this and actually never find that the relation is 100% accurate, but nevertheless of course it should give enough info for practical purposes.
Hello iron guys,
I have a quick question regarding grounding or not of the frame of plate chokes. I'm just wiring up a couple of Hammond 125C plate chokes, which are open frame and held by the usual C shaped clamps. Now, the whole of the clamp is coated with varnish so it's non-conductive. Why so? Is this an indication that the frame should be floating and not earthed? Or should I scrape away some of the varnish and ground the clamps to the chassis? Amongst other things, thinking of hum here.
Andy
I have a quick question regarding grounding or not of the frame of plate chokes. I'm just wiring up a couple of Hammond 125C plate chokes, which are open frame and held by the usual C shaped clamps. Now, the whole of the clamp is coated with varnish so it's non-conductive. Why so? Is this an indication that the frame should be floating and not earthed? Or should I scrape away some of the varnish and ground the clamps to the chassis? Amongst other things, thinking of hum here.
Andy
Hi Andy,
I generally make sure that each metal part is grounded. Saftey precautions would also recommend this practice.
This can also impact the frequency response depending on how the choke is wound.
This can be easily seen with a frequency sweep in both grounded and ungrounded condition. Depending on the construction of the choke, it can also have an influence which way around you connect the choke.
Best regards
Thomas
I generally make sure that each metal part is grounded. Saftey precautions would also recommend this practice.
This can also impact the frequency response depending on how the choke is wound.
This can be easily seen with a frequency sweep in both grounded and ungrounded condition. Depending on the construction of the choke, it can also have an influence which way around you connect the choke.
Best regards
Thomas
Reading David Davenport's article on Grounding, leads to the conclusion that it should be isolated from the chassis and "grounded" to the power common, like an output transformer.
btw I do have a pair of the plate chokes you referenced from eBay, and also a pair of the vt4c.com "200H 30mA" chokes, plus three pairs of big 78 lam chokes I had wound years ago. I never got around to trying any of them, especially not with a 26, but if you are interested you could test them out.
Simon
It's interesting to see where my plate choke experiments with the 26 started 8 years go. I'm now using NP Acoustics amorphous plate chokes which are the best I've tried so far. There are two available -
- 180H, 40mA, 1.15K DCR these are quite large, around 70x70x60mm
- 136H, 15mA, 2.1K DCR which are 50x50x40mm
The smaller one works well and is a slightly sweeter sound, the larger one is more detailed and would be my choice, though it's close. From the website it looks like they are both $120 each which is good value for amorphous cores. Shipping from Vietnam on top. The winder, Phuong Nguyen, is a very nice man and good to deal with, though he doesn't speak English. I think he uses an online translator for questions and communication, but that seems to work and I've had no problem getting the parts shipped. The specifications on the website seem different from the ones he gave me in messages, listed above.
Product & Price - NP Acoustic
Here's what I'm using now - I like the SIC diode bias. Running the 26 at 7mA seems to be OK for me, though I wouldn't go beyond that.
- 180H, 40mA, 1.15K DCR these are quite large, around 70x70x60mm
- 136H, 15mA, 2.1K DCR which are 50x50x40mm
The smaller one works well and is a slightly sweeter sound, the larger one is more detailed and would be my choice, though it's close. From the website it looks like they are both $120 each which is good value for amorphous cores. Shipping from Vietnam on top. The winder, Phuong Nguyen, is a very nice man and good to deal with, though he doesn't speak English. I think he uses an online translator for questions and communication, but that seems to work and I've had no problem getting the parts shipped. The specifications on the website seem different from the ones he gave me in messages, listed above.
Product & Price - NP Acoustic
Here's what I'm using now - I like the SIC diode bias. Running the 26 at 7mA seems to be OK for me, though I wouldn't go beyond that.
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Good question! If my memory is correct over 8 years, the following. All were used with FT-2 teflon coupling caps
- 2 x 156C in series. These were OK but not much more, and were prone to hum. Need to be shielded in some way really.
- Primary of LL1660. This was again OK, and with a teflon cap as good as using it as an interstage in 1:1
- No-name Asian plate choke, 50H and probably 30mA. This was better than the above and pretty good in fact. It suited the 4P1L nicely.
- 2 x 126C in series. These were really good, giving high inductance and 15mA current. Much better than a single one and also better than using the 126C as an interstage. A real contender
- Small NP Acoustics choke. This is amorphous and better than all the above, though 2 x 126C were close.
- Large NP Acoustics choke. This was marginally better than the smaller one and the best sound overall.
The last four options I would consider to be good solutions and better than the LL1660 in 1:1 as an interstage.
- 2 x 156C in series. These were OK but not much more, and were prone to hum. Need to be shielded in some way really.
- Primary of LL1660. This was again OK, and with a teflon cap as good as using it as an interstage in 1:1
- No-name Asian plate choke, 50H and probably 30mA. This was better than the above and pretty good in fact. It suited the 4P1L nicely.
- 2 x 126C in series. These were really good, giving high inductance and 15mA current. Much better than a single one and also better than using the 126C as an interstage. A real contender
- Small NP Acoustics choke. This is amorphous and better than all the above, though 2 x 126C were close.
- Large NP Acoustics choke. This was marginally better than the smaller one and the best sound overall.
The last four options I would consider to be good solutions and better than the LL1660 in 1:1 as an interstage.
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