I didn't get any with those value components.
I didn't get any with those value components.
"...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
That's good to know TJ. Let's see what happens, I'll go with the original component values.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
Yeah, you could use a 1MΩ bias pot if you liked but it would be nearly impossibly fiddly to use. The tiniest little movement and it'd move the bias voltage by a huge amount.
Not necessarily. It's the ratio that's important. (voltage divider)Originally Posted by ziess
So, if I upped the 25K to a 50K, I could go hotter, but not as cold; like shifting the range to be overall hotter?
The reason I ask is that there is so much of the range of that pot now that is basically unusable as it's so cold. It's up almost all the way to get to 69%, and the highest I can go is 71%.
Not that I want to go higher, but if I swap tubes in that need more, I'd like to be sure I can get there.
"...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
Try changing the 33k you have to 50k.
That makes it colder. I had to keep lowering that 33K down from 100K to get hot enough.
But I have a spare 50K pot, I think, and I have someone else that can use the 25K pot, so I was hoping to try that if it would work. I guess I should just try it and see.
Last edited by NTBluesGuitar; 04-10-2008 at 12:06 PM.
"...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
NawI guess there's no harm in trying the original spec 0.1uF and 220 k along with the HRD Bias circuit values. I don't really want to lose anything from the tone. If I get blocking distortion Rob will say "I told you so."
Pete
I know I've a slightly different amp to Pete but I certainly don't suffer any lack of 'tone' - the voicing is unmistakably vintage 'Fender' no matter what you plug into it... I personally think when he get's his bias in range things will definitely start falling into place - the B+ will certainly drop (mine dropped about 40V when I got it dialled in correctly) so... time will only tell
If I could find a road to get away it wouldn't be too soon....... Shipwreck Moon.......
That's right, I was thinking hotter meant more bias voltage.That makes it colder. I had to keep lowering that 33K down from 100K to get hot enough.
But I have a spare 50K pot, I think, and I have someone else that can use the 25K pot, so I was hoping to try that if it would work. I guess I should just try it and see.
The 50k pot will give more range. What DC value is coming of the bias diode?
40.1VAC before, and -54.3V after the diode. I'm at -31.6V put onto the tubes with the 50K trimpot in place.
I biased with the 50K trimpot in there and it's done what I wanted it to. I'm at 69.4% max plate dissipation and the knob is 2/3 the way up instead of 7/8 of the way up with the 25K pot. So, with 1.5K after the diode, a 50K trimpot, and 33K to ground, I'm where I wanted to be at 367V plate voltage and a B+ of 371.5V.
Hope those numbers help, Pete.
Very cool, and I read up and learned about voltage dividers in the process. I never really understood that concept until now, either.
Thanks, Joe!
"...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
OK Guys, heres an update.
Last night I changed the bias circuit components similar to TJ's. I used a 1.5 K, 22K pot and a 47 K resistor. (Didn't have a 33k). That seemed to cure the problem. I got up to -52 V. Now don't ask me what the range was because I forgot due to what happened later.
I also changed the coupling caps back to 0.1 uF and the resistors back to 220 K. Fired her up did a rough bias on the 6L6's. There was still a problem with the preamp as I got no sound and a quick inspection revealed a missing wire. OK ,connect missing wire and switch on. Lovely sparkling white noise...twiddle the tone controls and the hiss changes..this it....She's alive. Now I could tell just by that white noise that this is going to be one kick ass amp. It just sounded so much crisper and lively than what I was used to with the HRD, and that was with crap tubes. I was on cloud 9. Excited, I reached for my guitar and was just about to plug in when.......
The most horrible and very very loud noise came through the speaker. It sounded like a ships foghorn and I immediately had to flick the standby switch off for fear of damaging the speaker, my ears and not to mention my relationship with my neighbours.
I found the only way I could power it on to check voltages was to remove the Phase Inverter tube. So after a change of underwear I began checking the voltages. I found around 400 V on the grids of the phase Inverter where there should have been around 235 V.
Tracing that back to the power supply it looked like I was getting virtually no voltage drop across the two dropper resistors. I tested them and they seemed ok. By this time it was late and I was getting stressed. Went to bed and thought about it. This morning I snipped out 2 of the 22uF smoothing caps and checked them with my DVM. The one just after the choke was completely open circuit. That's what I get for re-using the caps from the HRD.
I've got a gig this evening and have to go there straight from work, but tomorrow I'm going to change all the smoothing caps. I only used them because the amp was still fairly new and they were rated at 500V. The ones I have are rated at 450 V.
However, those few brief moments when the amp was alive indicate that we're almost there.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
Where are you getting -52V? That should be enough....I'm getting -54V after the diode.
"...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
Hi TJ,
that was measured at the wiper of the 22 K Pot. I didn't note any voltages down. I was too busy stressin out over that blown cap. It wasn't until I slept on it and woke up suspecting the cap. I'm just slightly concerned that it wasn't coincidence and that it might happen again.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
At that wiper, I'm running about -34V there. My guess is that you're okay, as a higher negative voltage means colder bias, right?
-34V keeps my Winged C 6L6GCs in check at 69% max.
Have you measured cathode and plate voltage yet?
"...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
TJ, I did and I biased roughly at 60% of plate dissipation but I cant remember what the plate voltage is now. I was more concerned about the big foghorn I have built. I just did a quick check to make sure the component changes gave me a better ballpark bias control.
I'll get those caps swapped at the weekend and if they don't blow again I should have a working amp. It worked for a few moments before the cap died so the circuit must be ok. Once I have a stable amp I'll note the voltages and rebias.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
Did you try swapping the leads from the OT to the power tubes? That can often cure the sound you are describing.
That was my first thought too. Component failure would be the last thing I'd suspect in a new build after wiring errors, and bad solder connections etc.
Pete,
You say you pulled the PI tube, was the higher voltage with the tube out? Your not going to have the correct voltages if it's not in the amp. And did you mean to say 'plates' not grids, in reference to where you measured?
Yer - that happened to me too - swapped the anode feeds to the OT and hey presto - no more oscillation (foghorn
The voltages will settle down once you get the bias sorted and all of the tubes start consuming some of that B+ - the 'dropper resistors' only have effect with all the loads in circuit - I wouldn't get too hung up on measuring voltages - I did and Fezz's comment to the effect of 'it's a guitar amp, not a space shuttle' was appropriate! One successful build allays all of that over-thinking - you will get there...
If I could find a road to get away it wouldn't be too soon....... Shipwreck Moon.......
Another good point - I know you said you'd put a 1Ω resistor between both cathodes and ground a la the original HR schematic - I've put one in between each cathode and ground so I can always find out what the draw is on each individual tube - I find this very useful as I can then see how well the tubes are matched for current draw...
If I could find a road to get away it wouldn't be too soon....... Shipwreck Moon.......
Hi guys,
this morning I swapped out all the smoothing caps. The foghorn was still there but the voltages at the power supply were more what I expected so that cap was definitely faulty. The foghorn is just as loud now but without the harshness of ripple voltage. It's rather a nice foghorn now except you guys can probably hear it in the states I disconnected the 0.1 uF coupling caps to enable me to test with a full compliment of tubes. All voltages are as expected. My B+ is 420, bias is -38 mV.
Anode current is 92 mV at the test point and by my calculation that gives me about 65 % of maximum plate disipation.
I disconnected the wiper from the treble pot and reconnected the coupling caps. No foghorn. So the problem is in the pre-amp section.
Troubleshooting continues. I'll update you guys later.
Rob, I went for just one test point because even if there is an imbalance between the tubes there's not much I can do about it other than argue with the supplier. There's no balance control. I buy matched pairs and hope for the best. If I can find room to add another test point I might do it later though.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
I doubt the cap was faulty. You probably just put the tube back in and with current being drawn the voltages were normal. Have you reversed the OT leads at the 6L6 plates?
Fezz suggested I throw a couple in and I'm glad he did - you're right in that there's not a lot you can do once you've put em' (the tubes) in but I was amazed at how well certain suppliers match them compared to others... the Winged C's I got from CE Distribution were spot on to start and have drifted a coupla mV apart with use - so I've got them straddling the 70% dissipation mark (one a little hotter, the other a little cooler) - there's not a lot in it but I suppose the point is although you may not be able to exchange tubes once you've used 'em at least you'll know how well your supplier is looking after you... getting into the habit of checking the bias every now and then to see if any changes have occured satisfies my tendency to be a bit of a gear head and my curiosity about how long the tubes are lasting - I've pretty much been that way about anything technical...
Last edited by yankeerob; 04-12-2008 at 04:04 PM.
If I could find a road to get away it wouldn't be too soon....... Shipwreck Moon.......
JAM, that cap was definitely faulty. I checked it with my meter after removing the caps. I have a capacitance meter on my dvm. On resistance measurement you can see a cap charging from the meters internal battery. The other caps did, and that one didn't.
If I disconnect the treble wiper there is no noise. I have not reversed the plate connections yet but surely disconnecting the treble wiper proves that the fault is in the preamp?
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
OK, but it's a very rare case (and I've been into this for 40 years), and you mentioned the high measurements were without the tube, which should have been obvious that without current being drawn they would rise. I wouldn't assume disconnecting the treble wiper means the trouble is in the preamp, it may take some small signal to get the oscillation started. In any event if you reverse the OT plate leads and the oscillation persists you have ruled out the most common cause and can further troubleshoot.
OK JAM,
I'll try that tomorrow. Now it's time for
Thanks.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
Good idea. Have one for me too will you? (I'm still at work)Now it's time for
Pete
JAM,
You are a genius. I was sceptical about your idea of swapping the plate wires. I just cant see how that should make a difference but it has. I now have a working amp. Thank you. Must be something to do with phase. I can get on with the FX loop now.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
Woo-hoo! Another fine TFF project is working!!! Well done Pete
If I could find a road to get away it wouldn't be too soon....... Shipwreck Moon.......
Awesome!
Can't wait to see the finished job.
"...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
I wish I was a genius. It's quite common. (look at some Weber schematics). The negative feedback loop becomes positive when the OT leads arent on the correct sockets.
Anytime you get that sound on an amp with a negative feedback loop the first thing to try is swapping the OT leads. That sound will literally scare the s*&t out of you the first time you hear it coming out of your amp.
Well it's finished. Acouple of little things to sort out but the amp works. The FX circuit is not working properly but I have a bypass switch so no problem. When it is in circuit it doesn't seem to color the sound at all, just a slight drop in volume probably due to the fact that I have a 12AU7 in there instead of the intended 12AT7. (I had 2 of those which I bought on ebay but turned out to be faulty). I put in a treble boost cap on a switch a la Marshall JTM 45 and it works but it doesn't add much that cant be achieved by turning up the presence control and it is a little bit noisey so Im gonna remove it. The FX circuit I can fix at my leisure.
I think Rob is gonna build that effects circuit into his amp so between the two of us we can sort out the problems later.
I want to offer a big thank you to all the guys who helped me through this build. In particular, JAM, TJ, Wingnut1. Kapn, Zeiss etc. I must acknowledge that Wingnut was the first to suggest swapping the plate wires. I've only just noticed that. Sorry man.
A special thank you to our good friend Yankee Rob who supplied the turret boards and kept me informed about component choice, technical info, suppliers etc, and was there at the end of the phone when I needed him. Thanks guys.
Here's a pic.
http://images.lilypix.com/displayima...bum=2259&pos=9
Right that's the amp done, now "How do you play this thing?"
PS: Do you think I might have invalidated my Fender Warranty??
Pete
Last edited by Toneseeker; 04-14-2008 at 02:21 AM.
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
YAY!!! It lives!
What a feeling, eh? Mine is my favorite amp so far.
"...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
Hi TJ,
Just glad I can relax a bit now. It's got to be my favourite amp, it's my only one. Mrs TS is glad too. I've kinda neglected her during this build. Got some sucking up to do. Wonder how much that will cost me???
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
Outstanding! It's a great circuit, isn't it?
Got any gigs coming up where I might be able to pop along and hear it?
Tommy.
Hi Tommy,
nothing for a few weeks now. Not sure what's ahead. I'd need to check my diary but if there's something suitable I'll let you know. I may be rehearsing with a buddy of mine with a view to forming a new country band. If I can find somewhere local to rehearse you are welcome to come along and try the amp out.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
You guys have COUNTRY music there? It doesn't have bagpipes or anything there, does it?
...
...
...
...
...P.S. - I'm part Scottish, so it's not like I'm picking on you like that
"...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
With a name like Adamovitch??? your part scottish?
I don't do bagpipes. (Actually, my keyboard player has bagpipes on his synth which is handy now and then when we play weddings). I'm a real big fan of American country music. Favourites are Toby Keith, Wade Hayes, Gretchen Wilson, Vince Gill, Brad Paisley and George Strait, to name but a few.
There's not a great demand for it here and it's popularity is diminishing, but back in the 80's it was really big and there were clubs all over the place. The stuff I play for money is just general crap but my passion is country.
Pete
Failure is simply the opportunity to begin again, this time more intelligently.
Henry Ford
Hey toneseeker, the amp looks great. I'm sure you will enjoy it much more that the HRDlx. I thought of doing that with a blues deluxe I had, but it seemed to make more sense to sell the amp and buy a kit. Thanks for the acknowledgement about swapping the OT wires. I may have suggested it, but JAM was the dog with a bone that wouldn't stop pushing until you actually tried it. Congratulations and enjoy.
Tee hee...Scottish on my mother's side. Grandmother was Ethel Wanless (RIP).
The pollack in me comes from dad's side.
Anyway, good country is good music...hell, I'm in Texas, I oughta know. Let us know how the HRD-5F6 handles it!
"...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
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