NAD: Hiwatt Custom Super-Hi 50 (WITH CLIPS)

LP Freak":isxdub1s said:
Sounds like a pain in the ass to me
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It is. But it's ok, the amp sounds fantastic. Just gotta make sure to use a certain spec tube. Unfortunately you can't just throw in any old pair of EL34s. :doh:
 
^^^^
So the more negative feedback applied to the grid, the less current a given tube will draw. the rating on a given tube is based off of the amount of current it draws at a given voltage. The more current that a given tube draws the softer of a rating the tube will be given.

So if I am reading through this correctly the existing tubes are not drawing enough current and the amount of negative voltage applied to the bias is as low as it goes, a softer rated tube that draws more current is what is needed. This is the case we're increasing the bias resistor is not only be cheaper but the best option if you have multiple sets of tubes none of which can be bias correctly. I am curious what the bias voltage range is on this amp. I am not a big fan of specially buying tubes that are either too hard or too soft because I feel that they are closer to the edge of being not in spec. so from a design standpoint this is probably done so that tubes will never run too hot in this amp the alternative is to put in soft tubes to properly bias it but soft tubes in a metal amp is just wrong. You want headroom not early break up
 
scottosan":n5ucww0y said:
^^^^
So the more negative feedback applied to the grid, the less current a given tube will draw. the rating on a given tube is based off of the amount of current it draws at a given voltage. The more current that a given tube draws the softer of a rating the tube will be given.

So if I am reading through this correctly the existing tubes are not drawing enough current and the amount of negative voltage applied to the bias is as low as it goes, a softer rated tube that draws more current is what is needed. This is the case we're increasing the bias resistor is not only be cheaper but the best option if you have multiple sets of tubes none of which can be bias correctly. I am curious what the bias voltage range is on this amp. I am not a big fan of specially buying tubes that are either too hard or too soft because I feel that they are closer to the edge of being not in spec. so from a design standpoint this is probably done so that tubes will never run too hot in this amp the alternative is to put in soft tubes to properly bias it but soft tubes in a metal amp is just wrong. You want headroom not early break up
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Pretty much. I don't want a softer-rated tube because that = less headroom. Not what you want in a high-gain metal amp.

The DR504 has a 100K resistor from the B+ to feed the bias supply. This amp has a 150K. If I lower that down a bit, it might do the trick. But I'm going to see how the set of tubes I have coming sounds first.

I can check the negative bias voltage range and report back. The "range" is fine. But it's just shifted in the wrong direction to bias most tubes properly. Can't get the plate current low enough. So instead you have to run really soft tubes.

That said... hell... maybe they designed this amp to run super hot. Or to run super soft tubes? I sent Hiwatt an email about all of this but haven't heard back yet. I doubt it's supposed to be running an EL34 at 100%+ dissipation.
 
You have too much bias voltage You'd have to increase the 150k resistor to decrease -DC bias voltage which will effectively allow the tubes to draw more current
 
I'm glad you are getting the tone in your head with this amp but it kinda sucks that you are having issues this soon especially with that price point. It's a good thing you are a bit savvy with the inner workings of amps. I would be lost when it comes to troubleshooting an amp.
 
ClintN667":3foswyro said:
I'm glad you are getting the tone in your head with this amp but it kinda sucks that you are having issues this soon especially with that price point. It's a good thing you are a bit savvy with the inner workings of amps. I would be lost when it comes to troubleshooting an amp.
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I think it's more of a tube issue than the amp. That said... the bias range is limited.
 
New tubes are in. They biased up right in the middle of the bias trimmer's sweep. The amp definitely sounds different, but still close enough. Better than the SED =C= or Teslas, but not quite as good as the stock tubes that were messed up. I guess this amp just sounds better with an extreme bias mismatch. Now I can make some clips.
 
FourT6and2":2rqrxpcg said:
New tubes are in. They biased up right in the middle of the bias trimmer's sweep. The amp definitely sounds different, but still close enough. Better than the SED =C= or Teslas, but not quite as good as the stock tubes that were messed up. I guess this amp just sounds better with an extreme bias mismatch. Now I can make some clips.
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What tubes did you end up getting?
 
fearhk213":2oh4m218 said:
FourT6and2":2oh4m218 said:
New tubes are in. They biased up right in the middle of the bias trimmer's sweep. The amp definitely sounds different, but still close enough. Better than the SED =C= or Teslas, but not quite as good as the stock tubes that were messed up. I guess this amp just sounds better with an extreme bias mismatch. Now I can make some clips.
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What tubes did you end up getting?
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Same as the stock ones (JJ EL34).
 
FourT6and2":34hp2b17 said:
New tubes are in. They biased up right in the middle of the bias trimmer's sweep. The amp definitely sounds different, but still close enough. Better than the SED =C= or Teslas, but not quite as good as the stock tubes that were messed up. I guess this amp just sounds better with an extreme bias mismatch. Now I can make some clips.
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Looking forward to hearing it!
 
So SICK dood!!!!! Looking forward to some clips!!! Hopefully some Tool Undertow era riffs, like your Jose style amp build!! ;)
 
One of the most brutal, yet amazingly clear sounds I've ever had was my old '73 Hiwatt DR103 set dirty-ish, being boosted with a Kingsley Jouster.
I know exactly what you mean by your description of a high-gain AC30.
A lot of this is in the feel - Hiwatts are some of the tightest and most immediate amps you can play, thanks in no small part to the massive transformers.
I don't know how the new Hiwatts stack up to the old Hylight era stuff, but they just killed. Congrats on the new amp!
 
mhenson42":1xj4fb6j said:
Can you post a picture of the back panel?
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untitled_by_haftelm_dd0sdjz-fullview.jpg
 
Had a few minutes before work for a short clip. It's hard to record this thing accurately. Not quite what it sounds like in the room, but close enough.
I gotta say, the amp sounds better with the fucked up stock tubes. These new tubes that bias up properly sound softer and more fizzy. Still working on figuring that out.

 
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