Here is another thought for you..
Who in there right mind would use a 10A scale to measure mA..?
Or is it that it just gives a nice BIG fuse to ensure the tubes go before the fuse in the meter?
I would put a small value resistor (work out the voltage drop to give you the current you need) in the Gnd of the OP tubes measure the voltage across it divide by two to give you each tube..V/R=A set with the pot..With a very low value resistor you could just leave it in circuit...One in each tube leg would be better..OK you can't balance them because its just one setting for the bias..
Or find another dealer that will give you better information..
Regards
M. Gregg
Who in there right mind would use a 10A scale to measure mA..?
Or is it that it just gives a nice BIG fuse to ensure the tubes go before the fuse in the meter?
I would put a small value resistor (work out the voltage drop to give you the current you need) in the Gnd of the OP tubes measure the voltage across it divide by two to give you each tube..V/R=A set with the pot..With a very low value resistor you could just leave it in circuit...One in each tube leg would be better..OK you can't balance them because its just one setting for the bias..
Or find another dealer that will give you better information..
Regards
M. Gregg
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Thanks M Gregg, I tried to attach the PDF they sent me but this site said the file was too large so I took a picture of the relevant page. I thought I should run it by you guy's before I ventured inside the amp again. My meter manual says not to connect the ammeter across a voltage source so that was a red flag to me not to do what they said. The strange thing is, another thread I read somewhere said to do the exact same thing and the poster never got back with the results. Probably had a nice funeral service.
I wonder if they meant to unplug the transformer(plug 1 and 17) and actually connect the meter to the to terminals on the board. Or is that what you meant by stuffing the tubes? I'm not sure what that means. It sure is a confusing amp I bought. It should be relatively easy I would think.
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If you think about it..
The 400V B+ is on the board not the Tx so putting your meter across the connections on the board will short B+ to tube anode on each tube..
Yes the PDF shows that information...At the end of the day it depends on how much resistance is in series with the meter (regard the meter as short whan set to current ranges)..
I would ask the manufacturer for more information..
Unless someone here knows or can see any other things I'm missing...However its going to stuff the tubes with no load either in the anode or cathode..
If your talking to the manufacturer via Email send this and ask them to clarify it.
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Question regards amp bias.
Reason is if you set a meter to the 10A range it is realy a short between the probes just a low value shunt resistor in the meter..
So if you put your meter across the plug 1 & 17 you are going to short out the output Tx and burn out the OP tubes..same will happen on the 2 & 17 test..I could understand a voltage reading across the Tx and work out the current from the voltage reading..However you need to know the resistance value of the OP Tx or they need to tell you what voltage to set across the OP Tx..
If you remove the OP Tx and do the same test again you will stuff the OP tubes because there will be no load on the anode ie short circuit..
I think you need more information..The only way you can use the ameter is in series with the Op tx winding so the Tx resistance is still between the supply and the meter..Because plug 17 is the 400V B+ and the other two pins are the anode of the OP tubes..
From your link
http://www.freeinfosociety.com/elect...ew.php?id=2288
Ask the manufacturer if they can explain how this does not damage the OP tubes? Even if you can remove the Tx from the board and connect flying leads with the meter/ OP Tx in series, you still need the speaker load to prevent damage to the OP Tx.. (I bet they just measure the voltage (not current) across the Op Tx...)
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Please post the response..
Regards
M. Gregg
The 400V B+ is on the board not the Tx so putting your meter across the connections on the board will short B+ to tube anode on each tube..
Yes the PDF shows that information...At the end of the day it depends on how much resistance is in series with the meter (regard the meter as short whan set to current ranges)..
I would ask the manufacturer for more information..
Unless someone here knows or can see any other things I'm missing...However its going to stuff the tubes with no load either in the anode or cathode..
If your talking to the manufacturer via Email send this and ask them to clarify it.
----------------------------------------------------------------------
Question regards amp bias.
Reason is if you set a meter to the 10A range it is realy a short between the probes just a low value shunt resistor in the meter..
So if you put your meter across the plug 1 & 17 you are going to short out the output Tx and burn out the OP tubes..same will happen on the 2 & 17 test..I could understand a voltage reading across the Tx and work out the current from the voltage reading..However you need to know the resistance value of the OP Tx or they need to tell you what voltage to set across the OP Tx..
If you remove the OP Tx and do the same test again you will stuff the OP tubes because there will be no load on the anode ie short circuit..
I think you need more information..The only way you can use the ameter is in series with the Op tx winding so the Tx resistance is still between the supply and the meter..Because plug 17 is the 400V B+ and the other two pins are the anode of the OP tubes..
From your link
http://www.freeinfosociety.com/elect...ew.php?id=2288
Ask the manufacturer if they can explain how this does not damage the OP tubes? Even if you can remove the Tx from the board and connect flying leads with the meter/ OP Tx in series, you still need the speaker load to prevent damage to the OP Tx.. (I bet they just measure the voltage (not current) across the Op Tx...)
----------------------------------------------------------------------
Please post the response..
Regards
M. Gregg
I assume the 10A instruction is just playing safe and is standard teaching to people who have to use a meter but don't know what they are doing. You then switch down the ranges until you get a useful reading. That part of the instructions were probably written by the company lawyer.
Much better to roughly guess what is the maximum likely current and choose an appropriate range (200mA?).
Much better to roughly guess what is the maximum likely current and choose an appropriate range (200mA?).
I asked them this ? earlier:
thank you for the information. If I understand correctly , I should unplug plugs 1 and 17 from the board to break the circuit and connect the ammeter leads to the plugs(wires). thanks.
And their response was "yes"
I will ask them your question and hopefully they will respond, but I doubt it.
I really do appreciate your helping me with this and I agree that the most sensible thing to do is solder in a 1 ohm resistor temporarily between pin 3 and ground in case it keeps rising.
I got my new TADEL84-STR's and one of them was toast right out of the box. It figures, can't get a break. I double checked them in my Peavey Classic 50/50 and the same. While I was in there I did some checking with the bias probe and the same creeping bias was evident in the 50/50. It's basically the same design with the same stupid high voltages on the plate and pin 9. I don't think it's possible to really check the bias on these type amps with a bias probe. And I'd really be surprised if a resistor soldered directly to the socket would work either, but I'm willing to try. It's a major pain either way. I like big bottle amps. Never had a problem with them like this. And H&K are definitely retarded (I'm from Boston originally so no offense) telling me to adjust the bias on an unplugged tranny. It just doesn't make sense. No wonder they lost the war! Or maybe they're trying to get even????
You can check the bias with a resistor in the cathode of the tubes..
Just leave the transformer as it is (Plugged in) solder a low value resistor between the cathode of the two tubes and Gnd. Then measure the Voltage across it.
Then using Ohms law divide the voltage you have measure by the value of resistor and you have the current for the two tubes. Divide that by two and you have approx current for one tube..(the bias cannot be balanced just one set point)
So multiplying the expected current 17-20mA (This is one tube "assuming HK are correct" so its twice this) by the resistor will give you the voltage value you want..ie correct bias..
Regards
M. Gregg
Just leave the transformer as it is (Plugged in) solder a low value resistor between the cathode of the two tubes and Gnd. Then measure the Voltage across it.
Then using Ohms law divide the voltage you have measure by the value of resistor and you have the current for the two tubes. Divide that by two and you have approx current for one tube..(the bias cannot be balanced just one set point)
So multiplying the expected current 17-20mA (This is one tube "assuming HK are correct" so its twice this) by the resistor will give you the voltage value you want..ie correct bias..
Regards
M. Gregg
Hey I've just thought..
I cant see this amp but...are plug 1 and plug 2 on a flying lead from the OP Tx?
Then this would make sense...
You can only do one tube at a time and find a balance as close to the 20mA as possible maybe the 17mA would be a better point because one will be higher than the other if the tubes are not quite the same...
If they are on flying leads with B+ off you can disconnect the plugs one at a time (power off between) and put your meter between...remember you still need the speaker load to stop the OP Tx getting damaged..
Forget the B+ plug just unplug plug 1 and put your meter set to DC amps in between the plug and the board...The same on plug 2....then you can read the current...
I'm just wondering if its a miss print on the PDF when it should read plug 1 and plug 1 socket....plug2 and plug 2 socket ??????
Remember these plugs are near or at B+...so be careful...
If they are not on flying leads then the above post with resistor still stands..
Regards
M. Gregg
I cant see this amp but...are plug 1 and plug 2 on a flying lead from the OP Tx?
Then this would make sense...
You can only do one tube at a time and find a balance as close to the 20mA as possible maybe the 17mA would be a better point because one will be higher than the other if the tubes are not quite the same...
If they are on flying leads with B+ off you can disconnect the plugs one at a time (power off between) and put your meter between...remember you still need the speaker load to stop the OP Tx getting damaged..
Forget the B+ plug just unplug plug 1 and put your meter set to DC amps in between the plug and the board...The same on plug 2....then you can read the current...
I'm just wondering if its a miss print on the PDF when it should read plug 1 and plug 1 socket....plug2 and plug 2 socket ??????
Remember these plugs are near or at B+...so be careful...
If they are not on flying leads then the above post with resistor still stands..
Regards
M. Gregg
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I don't know what a flying lead is. Can you tell by the schematic or would you need a physical picture of the board and xformer.Hey I've just thought..
I cant see this amp but...are plug 1 and plug 2 on a flying lead from the OP Tx?
Then this would make sense...
You can only do one tube at a time and find a balance as close to the 20mA as possible maybe the 17mA would be a better point because one will be higher than the other if the tubes are not quite the same...
If they are on flying leads with B+ off you can disconnect the plugs one at a time (power off between) and put your meter between...remember you still need the speaker load to stop the OP Tx getting damaged..
Forget the B+ plug just unplug plug 1 and put your meter set to DC amps in between the plug and the board...The same on plug 2....then you can read the current...
I'm just wondering if its a miss print on the PDF when it should read plug 1 and plug 1 socket....plug2 and plug 2 socket ??????
Remember these plugs are near or at B+...so be careful...
If they are not on flying leads then the above post with resistor still stands..
Regards
M. Gregg
Flying lead...
The transformer is mounted then the wires from the Tx are perhaps 60mm long to a plug that then plugs into the circuit board..ie they are loose wires....so the Tx is not cast so the plugs are part of it..
Think leads from the Tx you can unplug without removing the OP Tx from the board..
What you need to be able to do is just unplug plug 1...and connect one lead of your meter to the plug and the other end in the socket on the circuit board..When your meter is set to DC amps it is a short so the B+ will go through the transformer (as normal) and then into 1st probe of the meter-through the meter- out of the other probe and into the tube anode. The circuit will be exactly the same as if the meter was "not their" because it is a short in current mode. It will read the current into the tube anode with the OP Tx in circuit as though the plug was connected. Just the meter between the plug 1 and socket for plug 1.
You can then reconnect plug 1 and disconnect plug 2 and do the same with plug 2 to read the current into that tube..so you will need to be able to disconnect Plug1 on its own then plug 2 on its own..
Remember to let the amp discharge before you touch the plugs Don't do it live. watch the probes don't drop off the socket or plug when live..Speaker connected as normal. Remember with the meter in this postion the amp would work as normal..don't use it while testing even if you want to see how much current is going through the tubes in case a probe drops of the connection..
Hope this makes sense. Post a photo of the OP Tx plugs ie what does plug 1 look like is it all wires into one plug or seperate plug 1 & plug 2?
Regards
M. Gregg
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here's the pictures. I got the replacement TAD's today. I figured I'd get some German beer to go with the German amp and German tubes. The blue wire is plug 1, brown wire is plug 2 and the red wire is plug 17. It would make sense to put the meter between plug 1 & board terminal and plug 2 and board terminal. Would you recommend setting the meter still at the unfused 10 A position? At least that way there's no fuse to blow and open the circuit providing it's not excessive current . What kind of current should I expect to see if I check it this way?Flying lead...
The transformer is mounted then the wires from the Tx are perhaps 60mm long to a plug that then plugs into the circuit board..ie they are loose wires....so the Tx is not cast so the plugs are part of it..
Think leads from the Tx you can unplug without removing the OP Tx from the board..
What you need to be able to do is just unplug plug 1...and connect one lead of your meter to the plug and the other end in the socket on the circuit board..When your meter is set to DC amps it is a short so the B+ will go through the transformer (as normal) and then into 1st probe of the meter-through the meter- out of the other probe and into the tube anode. The circuit will be exactly the same as if the meter was "not their" because it is a short in current mode. It will read the current into the tube anode with the OP Tx in circuit as though the plug was connected. Just the meter between the plug 1 and socket for plug 1.
You can then reconnect plug 1 and disconnect plug 2 and do the same with plug 2 to read the current into that tube..so you will need to be able to disconnect Plug1 on its own then plug 2 on its own..
Remember to let the amp discharge before you touch the plugs Don't do it live. watch the probes don't drop off the socket or plug when live..Speaker connected as normal. Remember with the meter in this postion the amp would work as normal..don't use it while testing even if you want to see how much current is going through the tubes in case a probe drops of the connection..
Hope this makes sense. Post a photo of the OP Tx plugs ie what does plug 1 look like is it all wires into one plug or seperate plug 1 & plug 2?
Regards
M. Gregg
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Well there you go its easy..
You can either put your meter in series with plug 17..ie unplug it and set the current for the both tubes ie 17mA X 2 or unplug plug 1 and put your meter in series with the conection on the board and the lead..then set for 17mA..(meter set for DC current)
use the bias adjust so its as I posted..
Err whats with the connections? look at the Tx diagram and the wires onto the tubes? LOL...we anyway its just put the meter in series with plug one or two and measuer the current..if you get any stabilty problems just put it in series with plug 17 and measuer the total current for the two OP tubes..
Normaly the middle connection is the CT of the Tx but its definatly input on one end sorry don't want to confuse you its just a bit strange..LOL
In easy terms unplug the blue wire and put your meter set to DC amps one lead on the blue wire and the other on its board connection...this will give current for one tube set to 17mA..the other should be close...if you get any problems then put the meter in between plug 17 and set for the two tubes togeather..remember its up at B+ voltage.
Regards
M. Gregg
You can either put your meter in series with plug 17..ie unplug it and set the current for the both tubes ie 17mA X 2 or unplug plug 1 and put your meter in series with the conection on the board and the lead..then set for 17mA..(meter set for DC current)
use the bias adjust so its as I posted..
Err whats with the connections? look at the Tx diagram and the wires onto the tubes? LOL...we anyway its just put the meter in series with plug one or two and measuer the current..if you get any stabilty problems just put it in series with plug 17 and measuer the total current for the two OP tubes..
Normaly the middle connection is the CT of the Tx but its definatly input on one end sorry don't want to confuse you its just a bit strange..LOL
In easy terms unplug the blue wire and put your meter set to DC amps one lead on the blue wire and the other on its board connection...this will give current for one tube set to 17mA..the other should be close...if you get any problems then put the meter in between plug 17 and set for the two tubes togeather..remember its up at B+ voltage.
Regards
M. Gregg
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Thanks M, I assume it has the flying xformer then. I was going to ask you if any of the connections would be the summ of both tubes but you answered my question. I thought it would be a continuous loop for both tubes no matter where the circuit is broken. Is this the actual cathode current that I would normally set at 70% of the tube wattage output? I'll make up some test connectors later and let you know the results. I can't understand why herr H&K didn't just explain it that way in the first place. The pdf they sent me was labeled "for techs only" so maybe they assumed I would know, but their directions were unclear just the same.
I guess you have done this before..
This is how I set bias...
17mA is 0.017A...on one tube assuming HK are at least correct on this point..
I put the meter in circuit and power up with my screwdriver in the pot.
Adjust very slowly. (small movements on the adjust pot.)
Then I watch the mA as the tube warms up and adjust the bias down as it comes up untill in this case it would be about 5mA then let it soak for about 10mins..
Then adjust the bias to 10mA wait 10mins and set to 17mA.
Soak test for about half an hour checking and adjusting if necessary.
Its safe to say that the HK information is complete cr*p..I hate to think the amount of power supplies and tubes that have been damaged by this information...If you get chance point this out to HK they should amend this dangerous info.
Any current that flows in the anode will be the same in the cathode.
Remember that plug 17 is the supply to the two tubes and is the only connection of the three that carries combined tube current, The other two are each tube.
Don't forget to have a load on the OP ie speaker or resistor.<<said it before...
Regards
M. Gregg
This is how I set bias...
17mA is 0.017A...on one tube assuming HK are at least correct on this point..
I put the meter in circuit and power up with my screwdriver in the pot.
Adjust very slowly. (small movements on the adjust pot.)
Then I watch the mA as the tube warms up and adjust the bias down as it comes up untill in this case it would be about 5mA then let it soak for about 10mins..
Then adjust the bias to 10mA wait 10mins and set to 17mA.
Soak test for about half an hour checking and adjusting if necessary.
Its safe to say that the HK information is complete cr*p..I hate to think the amount of power supplies and tubes that have been damaged by this information...If you get chance point this out to HK they should amend this dangerous info.
Any current that flows in the anode will be the same in the cathode.
Remember that plug 17 is the supply to the two tubes and is the only connection of the three that carries combined tube current, The other two are each tube.
Don't forget to have a load on the OP ie speaker or resistor.<<said it before...
Regards
M. Gregg
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I'm just going to leave everything connected and break the circuit at each plug. The spkr is soldered so it stays. I'll start swapping it eventually with some different Celestions. I have an old Sidewinder U.K. made that I'd like to try out. These new vintage 30 and other M. I. China ones are too raspy. Nice on the Cleans though.
I usually just measure the plate voltage, in this case on pin 7 and divide the 12 watts fo the EL84 by that and multiply the result times 70%. So in this case It would be 12/400x.70=21ma roughly. In this case I would think around 19ma would be pretty good. I guess theres also another way to do it factoring in the grid current but I would think this would be close enough. This amp as well a a lot of EL84 amps seem to kill it tubes with the crazy high voltages i guess.
H&K totally blew me off just like I figured they would. I'm still going to email them my results even though they won't have the courtesy to acknowledge it. Germans are weird. I worked over there for a few months in the 80's and they were quite anal.
Well M. , I finally checked it out and thanks to you, problem solved!!! The meter between plug 1 and the board terminal adjusted up to 20ma where I wanted it and stayed there nice and steady for as long as I kept it on. Plug 2 read 19.7 ma. This version amp has a balance pot so I adjusted it to 19.8ma.Grid current should be negligible…. it will be close enough.
You will probably have one tube a little higher or lower than the other there never a perfect match.
Regards
M. Gregg
I just want to thank you again for sticking with me and helping me with this through the finish. You are a great guy and an asset to this wonderful forum.
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