I put a 470 ohm on V5 between pins 1 and 6 instead of a 470K ohm. The voltage wasn't being dropped across that resister. I don't know if that's what is causing all of my problems, but I'll let you know after I change it.
I put a 470 ohm on V5 between pins 1 and 6 instead of a 470K ohm. The voltage wasn't being dropped across that resister. I don't know if that's what is causing all of my problems, but I'll let you know after I change it.
Cool, it could something easy - yea!
It's always something stupid like that!
I once used the wrong value resistor at the bottom of a BF tonestack. I was building to order ASAP and couldn't work out why the amp had a ton more gain than it ought to and why the tone controls were crap meanwhile the guy is getting on at me to finish his amp!
Turns out I'd inadvertently added an uncontrollable raw control.
Tommy.
At least you figured it out. I once built an amp and couldn't figure out why it had so much gain, crappy sounding gain at that. I finally took a bias reading and then dramatically changed the bias resistor value - way off spec (cathode biased amp). The amp has been fantastic ever since, but I still dunno why I had to do that, LOL!
I changed the resister and the Vibrato is more pronounced, it isn't like the opto-oscillator version thought. Someone mentioned a mod that increased the intensity so I might have to look at that. It still doesn't seem quite loud enough so That is something that I still have to look at. I used crimp on terminals for the speaker connections and I'm wondering if that could be an issue? I'll have to keep working on it till I figure it out.
No, the spade clips shouldn't be an issue. I use em from time to time. Check those voltages bro! The trem mod is a David Allen thing. I'll see if I have any notes on what value to use.
I swapped the connections to one of the speakers and it added some of the high frequency sparkle that was missing. The Vibrato is a little more pronounced. I'd still like to take a look at the David Allen mod.
I've checked all the voltages except V6 and while they are low they are proportionately low and I think that is because of my bias. I biased it at 70% and I've never seen plate voltage drop as fast as current went up with any other amp. I think I'd have to take bias down to 50% to get the voltage up near 440 volts. I could also use the 120 volt tap off the PT instead of the 125 volt tap and that would up my voltage as well.
The other thing that could be affecting output is the OT. If you remember I went with the smaller OT to get more OD and that could be affecting my output. I'll have to get Jerry the geezer over and get his opinion.
No, we used the 'smaller' OT (old stock one) and our amp screams. In fact, it's obnoxiously loud. Yeah, maybe the tap you used is the culprit. Or maybe it's the PT...? You sure your power tubes are good? And your pre-amp tubes as well? BTW, refresh my memory - what speakers do have in there?
Oh yeah, Allen's 'secret trem mod' is just using a 470K resistor instead of 1M coming off of pin 1 of V4 (or is that V5 on your amp?) - essentially halving the value...
I have a 10F150 and 10A150 in it. I sent you an email with my voltages attached.
couldnt open the zip file on this computer (Mac-top) :-(
should be a perfect spkr combo, maybe a tad warm for others - but i'd dig it
Zip files ought to work just fine on a Mac...
Try right click>open with> choose an app.
Uh OK, but we're talking dinosaur here LOL
nope just keeps downloading over and over
You need to download it to your computer to open it.
V4 is the reverb recovery just like in the BF amps. Pin 1 of V5, the tremolo tube, is connected to a 470K (which connects on the other end to pin 6) in the bias vary tremolo.Originally Posted by Gris
Pin 3 of V5 in the bias-vary trem connects to a 1M resistor as well as a .022uF cap. Is that what you're referring to?
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
Yeah, I was thinking of my PR I modded that way per suggestion. I'll have to look at that AA964 schem again. BTW, I have dyslexia so double check EVERYTHING I say always, LOL.
edit - scuse me 1164. just looked at the Weber version (cant read fender's on this puter) and it's pin 1 on there - goes to the intensity control via 1M res and 0.1 cap...
oooh, just looked at Ted's 6G16 - the vibrato circuit is all different. i'll need to think on this a minute... guess it's cause the Princeton only has half a tube there
anybody got a link to the brown VV schem - legible?
Last edited by Gris; 03-02-2009 at 03:17 PM.
Shouldn't be a zip file Gris, it's an Excel spread sheet.
i'll get my daughter to do it on her puter when she gets home or at work tomorrow worst case
I changed to the 120volt tap and re-biased for 60% max plate dissipation, it increased the plate by 30volts and voltage at A & B by about 30 volts. It has given me a little more clean headroom, but not a lot more volume. If I use the diode rectifier, 6 1N41007, will that increase my voltage and allow me to bias hotter? Should I be looking elsewhere for my volume issues? I guess I should have Jerry over and get his opinion on the volume.
Why don't you try it out with two of the speakers in your 5F6-A?
That should at least eliminate the speakers.
Tommy.
That 10F150 should be loud as all get out. I'll have my guru look at the voltages. But wait you have new ones now. Send those.
If you send them to me I ought to be able to open them and forward them the Gris.
Tommy.
Cool, got that email.
Mark, I'll pass them on to you.
This amp uses 6L6GC outputs, right? 431VDC on the plates and 16mA = bias that's waaaaaaaaaaay cold. Or am I missing something?
Where are you getting 16 mA on the bias rite it was 42mA.
From that Excel doc. Going by the figures on that your output tubes have a static plate dissipation of around 6W per side.
Can you lead me through the calculation? I'm not seeing where you are getting the 16 mA. I measured it with a bias rite and it was 433 VDC and 42 mA current per tube. That's 17 watts per tube which is about 60% of max plate dissipation. I am not biasing them at 70% because the bias is going to vary up and down with the vibrato and I wanted to play it safe.
Well, on that Excel doc you sent to me both the cathodes on the powertubes read 0.016VDC (V). Assuming that reading is to ground through the usual 1Ω resistor (R) we can see that the cathode current (I) is 16mA (I=V/R=0.016/1=0.016A=16mA).
Where wattage (W) = V (in this case plate voltage or vP) x I,
W = 431 x 0.016 = 6.9W.
Subtracting a little to account for screen current your tubes are dissipating 6W at idle.
No need for a Bias Rite, just some sums! Perhaps the figures are wrong though. If it were biased this low it'd certainly explain your low output.
Tommy.
Tommy, I don't know where that number came from. It's not on the copy of the spreadsheet saved on my computer, but I opened the attached file I sent to you and I can see what you are talking about. I don't have 1ohm resisters from the cathode to ground because I have a Weber Bias Rite that I use to bias my amps. You can see the numbers I got in my prior post. Again I don't know where that number came from as it isn't on my copy of the spread sheet.
Ha ha, cool! Well at least you've eliminated mis-biased tubes!
That's true, I'm going to ditch the spade terminals and just solder the wire to the speaker terminals and see if that makes a difference.
I didn't get the second spreadsheet, with the 120 tap...
I sent them to you this morning Gris.
Got em. Hey we can have a race! I'll see if Jer and I can you straightened out before NTB gets Hippiebob done, LOL! Will call you tonight... :-)
Too late, Hippiebob's already done, up and running.
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
Mines up and running and totally usable, I'm doing what I like to think of as fine tuning.
Sorry for not emailing that to you, Mark. Family emergency involving hospitals took over today I'm afraid.
I think I may have a bad output jack or a short in my OT. The tip of the output jack has continuity with ground. I don't think that should be the case. Any input?
It's the OT, I took the 8 ohm tap off the output jack and it reads o ohms between it and the black ground tap. Could this be why I'm getting low output?
Absolutely would be low output if a bad OT. Did you try another tap to make sure it's the winding and not just the wiring...?
No I haven't. Maybe I'm off here and there shouldn't be any resistance between the two windings. I'm just searching for why the low output.
Each winding should have a separate static resistance, they usually differ by a little. Pull the OT and take readings off each winding out of the amp. Wait hold on let me look at something before you pull it.
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