I just looked at the board from the top view and it is somewhat transparent so it looked like 1 and 6 were connected to nothing and 3 was which might be ground . I didn't want to blow my meter ohming around in case some of the caps were charged up and to remove the board to see the underside is a major dismantling.
If it works, keep the 6P15Ps, they are rather cheap. You can get 8 for $31.
6P15P-EV = EL83 = SV83 Pentode tubes, NOS, Reflector, Original packaging, 80s | eBay
6P15P-EV = EL83 = SV83 Pentode tubes, NOS, Reflector, Original packaging, 80s | eBay
Obviously the 6P15P's are quite robust, considering the voltage in that amp, but I'd be looking for a pair of 6P14P-EV's to try.
jeff
jeff
that's really what I want to do anyway, put regular EL84's in there but I wanted to make sure that they would work or if I needed something that is rated for 400v like TAD str's of EL84M's.
The other thing that puzzles me is why H&K refers to this amp as having EL84's rather than EL83's. And why they put them in without the aforementioned mods that are needed for them to properly work. As I said, I'm a newbe to tubes so is this amp actually a typical EL84 design going by the schematic?
They work but I'd rather not use them if the amp isn't designed for them and even though they seem to sound pretty good it seems like an odd tube (video)to have used and I'd rather try a traditional EL84 if nothing else for comparison but I wanted to make sure they didn't mod this amp for EL83's.
With pin 3 (cathode) grounded, measure the resistance between pins 1 and 3. If it's zero, you'll have to remove what ever connects to pin 1, then you can use EL84s, but probably can't use 6P15Ps. I bet they installed 6P15P-EVs because they can get them for less than half the price of 6P14P-EVs. The internal construction is almost identical, except for the screen grid.
I don't know what would happen if you left the suppressor grid floating. It didn't work too well when I left it floating on a set of GU-50s.
6SN7 was used as verticle oscillator and verticle deflection amp in TVs.
I don't know what would happen if you left the suppressor grid floating. It didn't work too well when I left it floating on a set of GU-50s.
6SN7 was used as verticle oscillator and verticle deflection amp in TVs.
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I'll have to check again but I don't think pin 1 is connected to anything. What happens when an EL83 is just installed in an EL84 amp like this was? Would it still sound normal. H&K said to put any EL84's in it so they must've just directly substituted the EL83 for the 84.
EL84's don't use pin #1 for anything, so no surprise if it's not connected.
Good Question. You said pin #6 was grounded, so obviously someone was thinking ahead.
Yup.
jeff
thanks for those ? finally answered. One other thing I was wondering about is biasing the amp. One nice thing about it is the bias pot. Someone suggested placind the meter in ma across (plug1 and 17) and (plug 2 and 17) and that it should read about 20ma. I put the meter across there and it read a lot higher than that and besides I thought to read amps the circuit has to be broken. I was thinking of making up a bias tool with the 1 ohm resistor. just not sure which pin it goes to.
Yes, the ammeter is in series with the load. You can measure voltage across a resistor and calculate the current.
The resistor would go between pin #3 (cathode) and ground.
jeff
thanks Jeff. I appreciate your help as well as all the others. I knew this was the best forum to get the right help. I'm so glad you guys offer such good advice.
Forgot to ask, do you think any el84 would be ok or should I go with one rated at 400v.
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Some EL84s and 6BQ5s have pin 1 and pin 2 tied together. There are alot of variances in the EL84 family. 6P14Ps don't connect pin1 to anything except the lower mica plate, same with newer JJ EL84s.
6BQ5s and EL84s are rated for 300V on the anode. Alot of amps ran them up to 370 or so, but at 400 they could arc, you can try. 7189s are rated for 400V, but don't use 7189As, because they have a slightly different pinout. You can use Russian 6P14P-EVs, or EL84Ms.
I'd be inclined to make the same recommendation, although some of the amps surely came stock with JJ's. Not sure if the 20th anniversary is the same amp?
Hughes & Kettner 20th anniversary Tube Amp Demo - YouTube
I took a quick glance thru the manual. Matched pairs of output tubes are recommended.
jeff
Hughes & Kettner 20th anniversary Tube Amp Demo - YouTube
I took a quick glance thru the manual. Matched pairs of output tubes are recommended.
jeff
I was hoping to try JJ's in it too. I believe the TADEL84STR's are rated for 400V and I really like their 6L6GC-STR's so maybe I'll try a pair of those. I still might try the JJ's briefly just to see how they sound if they don't red plate.
NO NO NO!
6P15 is NOT an EL83. EL83 and SV83/6P15 are totally different tubes!
EL83 has a 9Watt plate and different pinout. EL83 is not made anymore!
6P15/SV83 is almost the same as an EL84 and makes a perfect drop in replacement, unless the circuit is high stress, in which case a higher screen resistor is needed, but that is all. The supressor grid is not tied to cathode in the 6P15/SV83, but you can just float it without doing damage. Packing a 1uF cap between pin 3 and either 1 or 6 makes for a sonic marvel, and EL84 can still be used as is.
Jeff,
Fixed bias design.
With a plate to cathode voltage of 402V and screen voltage of 399V you will be better off looking for 6P14P-EV, Sovtek EL84M or 7189 tubes. (Unfortunately scarce and expensive at the moment). I’m not familiar with TADEL84STR's. Depending on the actual quiescent current through the tubes 6BQ5s may work, but only if the dissipating ratings are observed with a safety margin. However, this is not a risk I would take on this amp, if it were mine. (BTW, what current are you running through the 6P15P tubes - how do you set the bias on this amp.)
I agree with Iapratho that SV83 is incorrectly rated for 200V max screen voltage (should be 330V at 1.5 watt) and that 6P15P-EV could be used in some situations to substitute a 6BQ5, but I don’t believe this is one of them. Here you are looking for a 7189 substitute. (That opens another can of worms, because 7189s might be identical in build to 6BQ5, but will leave that for another day).
Fixed bias design.
With a plate to cathode voltage of 402V and screen voltage of 399V you will be better off looking for 6P14P-EV, Sovtek EL84M or 7189 tubes. (Unfortunately scarce and expensive at the moment). I’m not familiar with TADEL84STR's. Depending on the actual quiescent current through the tubes 6BQ5s may work, but only if the dissipating ratings are observed with a safety margin. However, this is not a risk I would take on this amp, if it were mine. (BTW, what current are you running through the 6P15P tubes - how do you set the bias on this amp.)
I agree with Iapratho that SV83 is incorrectly rated for 200V max screen voltage (should be 330V at 1.5 watt) and that 6P15P-EV could be used in some situations to substitute a 6BQ5, but I don’t believe this is one of them. Here you are looking for a 7189 substitute. (That opens another can of worms, because 7189s might be identical in build to 6BQ5, but will leave that for another day).
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