rknize said:
I have a 10W 10k that I was planning to put in place of R6. It's a big thing - so I might have to be creative on getting it to fit without getting too close to the cap.
Hmm data sheet says 300b's draw 1.2A each for heater current and 300ma for the 5842. Err, that adds up to 3A...
Actually I don't see how D4 & D5 do anything since the center tap isn't grounded... where is the current path?
And here are some temp readings - all in F.
R6 - 157
D4 - 146
D5 - 184
D1 - 207 *toasty*
V1 - 131
I took my 13mm wrench off and replaced it with a big pentium heat sink - but I had to use two washers to get the spacing I needed. Probing around D1, it's heat sink, the washers - it looks like the heat transfer from D1 to the first heat sink it just inefficient. I may toss the small heat sink and connect it directly to the big one. Hopefully the problem isn't the mica insulator, because I'll need that...
Anyone know of any thermal epoxy I can use? Cheap is preferred.
R6 - 157
D4 - 146
D5 - 184
D1 - 207 *toasty*
V1 - 131
I took my 13mm wrench off and replaced it with a big pentium heat sink - but I had to use two washers to get the spacing I needed. Probing around D1, it's heat sink, the washers - it looks like the heat transfer from D1 to the first heat sink it just inefficient. I may toss the small heat sink and connect it directly to the big one. Hopefully the problem isn't the mica insulator, because I'll need that...
Anyone know of any thermal epoxy I can use? Cheap is preferred.
rknize said:
I was very careful to put the laser on the body of both devices. U1 definitely measured cooler than the diodes. I could be wrong - but I measured it several times, and they always came up the same. I suppose a thermistor would be better... used to have one of those somewhere...
I wondered about that, but that would make C2 useless... but you *have* to be right since D4 & D5 are obviously conducting current.
One thing my dad taught me was to never draw a cross in a schematic ... it confuses people! These days I always insist that anyone drawing a schematic, that I will use, put a dot or some kind of indication that there is a connection in the drawing.
Wonder if George would mind if I redrew that for him
oldmanStrat said:
It might be how it is packaged, but I'm pretty sure it's the regulator. Schottkys typically only drop .4V while the regulator is dropping a volt or two.
oldmanStrat said:
Yeah, C2 is useless in the 300B config. In the 45 config, those diodes become a half-wave bridge for a negative power supply that is used to kick-up the 3.15VDC coming from the other half back to 6.3VDC for the 5842 heaters. That's probably why he didn't bother using a better diode there...in the original design it was only powering the 5842 heaters.
oldmanStrat said:One thing my dad taught me was to never draw a cross in a schematic ... it confuses people! These days I always insist that anyone drawing a schematic, that I will use, put a dot or some kind of indication that there is a connection in the drawing.
Wonder if George would mind if I redrew that for him
LOL...my dad said the same thing when I was a kid. Even with the dots, they can be put there by accident. That was back in the days of hand-drawn schematics. Now they typically come from a CAD program that would have caught such an error. MJ uses that same old style and I found myself tripping over his schematics too. Oh well...
rknize said:
yes but all of the heater current is passing through both of the diodes - 3A @ 5V - 15W in that TO220 package... seems like it would get hot to me. I have no idea how much current the -150V draws.
[edit]
ick - if they both only drop .4V then we are looking at .4 x 1.5 x 2... not a lot of wattage. doesn't explain the measurement...
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rknize said:
isn't it great when your dad is finally right? The one thing I like about DxDesigner is that it forces you to put a junction (connection) when wires cross - or it issues a warning. Don't remember if Eagle does that too. The problem with Dx is that it is sometimes hard to tell the difference between a dot, and a box (which is a floating node) been caught there too...
Today I got the holes for the top cover done - or initially. One of them was off just a bit, enough that I'll have to punch a larger hole to compensate. Don't really want the tubes touching the top plate.
I still need to put the motor run cap in circuit and figure out the final heat sink - I'm just not happy with the one I have and it's attachment.
I am so very tempted to bring the amp to down to my office and check it out on some nice speakers. But once I do that I know it will be a looong time before I finish what needs to be done.
It is amazing how good it sounds with those little KLH speakers. It's just not very loud. And of course there is no bass.
I still need to put the motor run cap in circuit and figure out the final heat sink - I'm just not happy with the one I have and it's attachment.
I am so very tempted to bring the amp to down to my office and check it out on some nice speakers. But once I do that I know it will be a looong time before I finish what needs to be done.
It is amazing how good it sounds with those little KLH speakers. It's just not very loud. And of course there is no bass.
Attachments
Ok decided to break my rule and try it out on my 94db speakers.
Hmm, I have to crank the volume all the way to get a reasonable amount of sound out of it.
What is the recommended bias for the 300b's? I'm at 60ma now.
Damn this amp is quiet! Ears right up to the speakers, and I'd swear it was off...
Hmm, I have to crank the volume all the way to get a reasonable amount of sound out of it.
What is the recommended bias for the 300b's? I'm at 60ma now.
Damn this amp is quiet! Ears right up to the speakers, and I'd swear it was off...
Insufficient idle current should not cause the apparent total lack of gain he is seeing. I accidentally ran a pair of single ended 6B4G with about 100 volts on the plate and 15 mA idle current (they should be ~300 volts and 50 mA). They sounded alarmingly normal at normal volume levels, providing adequate volume for background listening.
I think he's got the signal shorted to ground at the input, the output, or somewhere in the middle.
I think he's got the signal shorted to ground at the input, the output, or somewhere in the middle.
Just to make sure that I'm clear - it's plenty loud - but it certainly isn't shaking the plates off of the wall on the next floor. That was sort of my expectation.
This amp is using trancendar OPT's with 5K impedance and no UL tap. I'm comparing it to my SSE with the monster Edcor OPTs and UL... It may not be a fair comparison.
On my SSE I generally only turn it up to 1/2 to 3/4 before I start thinking - yeah too loud. It's all the way to 9/10 on the SE when I'm thinking that is about right.
Ok, and BB just came on (I like to live the love that I sing about), and yes he sounds great. Changed the bias to 75ma, didn't seem to affect the volume.
So far this amp is quieter and has more detail... but the SSE shakes the room more. Especially with the KT88's...
This amp is using trancendar OPT's with 5K impedance and no UL tap. I'm comparing it to my SSE with the monster Edcor OPTs and UL... It may not be a fair comparison.
On my SSE I generally only turn it up to 1/2 to 3/4 before I start thinking - yeah too loud. It's all the way to 9/10 on the SE when I'm thinking that is about right.
Ok, and BB just came on (I like to live the love that I sing about), and yes he sounds great. Changed the bias to 75ma, didn't seem to affect the volume.
So far this amp is quieter and has more detail... but the SSE shakes the room more. Especially with the KT88's...
ACK - found the problem - I have a bad 5AR4 !! Only half of the tube was working... This makes a lot of sense since D4 & D5 were measuring significantly different temps. It may also explain D1...
I noticed that one of the filaments on the rectifier was NOT glowing at all, but the other one was very bright. Swapped it out with the one from my SSE - and the bias was waaay off !
Reset the bias, and now I have some volume...
Now if I can only get the tube vendor to refund my money...
[edit]
I have an old GE 5U4GA that I was considering trying as a replacement for the 5AR4... good idea? Bad?
[/edit]
I noticed that one of the filaments on the rectifier was NOT glowing at all, but the other one was very bright. Swapped it out with the one from my SSE - and the bias was waaay off !
Reset the bias, and now I have some volume...
Now if I can only get the tube vendor to refund my money...
[edit]
I have an old GE 5U4GA that I was considering trying as a replacement for the 5AR4... good idea? Bad?
[/edit]
oldmanStrat said:
The 5U4 should drop in for the 5AR4, but is directly heated (so quicker warm-up) and will drop more volts.......According to TDSL, the 5U4GA PIV =1550V with a 44V drop at 225ma compared to PIV=1500 for the 5AR4 (I couldn't find the voltage drop for the 5AR4 in my quick search) so it should be plug and play with lower output volts.
Edit: the 5AR4 is rated for 550-0-550 V in and 160 ma I rectified, and the 5U4GA is rated for 450-0-450, and 250ma I rectified, so it should work fine with lower volts out and maybe a little noisier from being directly heated.
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