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Can anyone recomend a suitable replacement for this transformer? This is an old double R core which has flashed over.
(1400VCT secondary is a bit much though, Orange)
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Can anyone recomend a suitable replacement for this transformer? This is an old double R core which has flashed over.
(1400VCT secondary is a bit much though, Orange)If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time. -
Just curious, what's a double R core? Pictures and amp schematic?
If you change the rectifier to bridge type you could use a 700V (2x350V) PT.
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I don't think a double "R" core exists. I meant to write "C" core, but it looks a normal C core.Originally posted by Helmholtz View Post
If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.Comment
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If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.Comment
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Yes, it looks like a double C core. I think a C core is always a double C core as the tape wound core needs to be cut into two "C" shaped halves to allow mounting of the coil formers.Originally posted by SoulFetish View Post
(An E/I core replacement would need to be bigger).
Schematic links don't work.Last edited by Helmholtz; 06-17-2020, 12:58 PM.- Own Opinions Only -Comment
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Same here. I wish whichever browser or OS is pushing the webp format would just quit. Many older systems do not support it.Originally posted by Helmholtz View Post
Here is a converter that will change it up to a jpg, I'm sure there are other online converters as well.
https://convertio.co/webp-jpg/
Originally posted by Enzo
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If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.Comment
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Still wondering about the actual B+ in these amps. KT88s have a plate voltage limit of 800V. 700VAC should result in a B+ considerably exceeding 800VDC.- Own Opinions Only -Comment
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I don't think the HT will be over 800VDC due to the action of the choke between the rectifiers and the first filter cap. The actual value rather depends on it's inductance, but assuming something big to suppress ripple has been chosen that it could easily be around 630VDC. The unloaded output voltage is the average on the input e.i. 0.9 * 700 = 630VDC.
Have you tried talking to Orange? Otherwise it's a custom wind I suspect.Experience is something you get, just after you really needed it.Comment
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Nick is right. I don't think this amp is working over 600V around. I found this UL configuation works in british amps at beginning at '70 as well in Marshall 200 or Simms Watts 200. I currently work into a Simms 200. The supply shows me 700V dc around with no load but goes under 650V at iddle and 580V at nominal power , which put the output tubes within their specs. In my PS was more than 20V dropped over the choke due to its internal resistance. At this voltage 4xkt88 draw 700mA around at full power into a 2500 ohm load. I think a more common Hiwatt 200 style replica PT (285+175V/1A) will work well with both secondaries series tied (not sure by its physical size; a C core is supposed to be more efficient than a E+I at same size). You should use a bridge rectifier instead. Look at 1n5408/150A surge.A secondary PT 10-20 ohm resistance will help to limit the startup surge, so no limiter resistor need it.
JJ kt88 works well at 600V. I will replace those 270 ohm screens to to 470 or 1K maybe if the ap is intended for serious drive...Last edited by catalin gramada; 06-18-2020, 08:32 AM."If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."Comment
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What this mod will be about? Further moved "fry" point? Can you explain?Originally posted by catalin gramada View Post
Any change in sound? Downsides?
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It.s not a mod, but a safe measure to not toast the tubes.Overdriving power tubes supplied at this voltage (600V arround) will determine to dissipate 20w around or more by the screens with 270 ohm limiter...as I remember...No good. The datasheet list 8 W arround . From my limited experience I keeped 12w as a limit...Of course little bit of attack will be loose. If you intend to play the amp clean or, overdrive just the preamp, 270 ohm will not be an issue. Remember is a ultralinear. The screens are supplied at the same voltage as the plate. You have to give a chance to limit the current somehow when screens start to draw.Originally posted by boroman View PostLast edited by catalin gramada; 06-20-2020, 04:45 AM."If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."Comment
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I see. I have one and considered full re-cap, re-bias and checkup after all those years, that's why I'm askingOriginally posted by catalin gramada View Post
So, playing hard bass with the one is risky with the 270R? I could put 470R but I'm wondering if it'll be any difference in the sound when amp is pushed hard?
Also, how to bias it properly? What were your readings?
These aren't popular amps, so I'm glad that someone actually own this amp here...Comment
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There are not so popular cause this design was not intended for MI aplication. It comes from hi-fi world as Wiliamson derivates. GEC proposed some designs based on kt88 tubes, which was their invention btw. and some companies just gave copy/paste. I.m not convinced by their reliability, lot of failures around when try to drive hard the power stage but there are nice powerfull clean amps (mine Simms shows a perfect sine at 220w rms before clipping at 580v as low as 35cps. You can get overdrive from preamp without to endanger the power stage...and think most useful mod for this amps is to install a ppimv master volume as most users did.
late edit: I burned myself two tubes during my hard tests with 470 ohm into the screens. Was happened very fast, no time to cut off. I expect a new quad this days...not so funny. My curiosity cost me almost 200 bucks...There are days I was sorry I woke up...
Last edited by catalin gramada; 06-18-2020, 09:27 PM."If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."Comment
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Found for full wave swing choke input : I dc = 1.54 x I sec. ac. 0.325x1.54= 0.5A
Hammond have 700 series only for the plate. https://www.hammfg.com/electronics/t...00?referer=787
You can hang on a 6v transformer for heaters somewhere in the box...Last edited by catalin gramada; 06-19-2020, 04:26 AM."If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."Comment
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