Did any of you guys have trouble with a 60hz hum? I didn't notice it at first but now that I have, it is annoying to say the least.
Actually the more I dig into this, I think it may be a grounding issue. I rewired my rca inputs and grounded the shield on one end. It had no effect. Its just odd that both units are doing the exact same thing. Almost feels like it power related. Definitely more pronounced when running through my preamp than if I plug directly into the amps with my iphone.
Actually the more I dig into this, I think it may be a grounding issue. I rewired my rca inputs and grounded the shield on one end. It had no effect. Its just odd that both units are doing the exact same thing. Almost feels like it power related. Definitely more pronounced when running through my preamp than if I plug directly into the amps with my iphone.
So I am a bit frustrated with this hum issue. I have rewired my inputs exactly the way Pete suggested, using unbalanced guitar cable using the shield as ground. I tried lifting the ground on the on the power supply with no impact. They are totally silent when I plug directly into the amps from my laptop or iphone using a stereo to rca cable but as soon as I connect an actual preamp (and I have tried 3 separate units with different tubes) I pick up a bad hum. I have confirmed that the chassis are properly grounded
So embarrassing as this is to admit. You were entirely correct. It seems it was nothing more than a bad cable. Not sorry that rewired the inputs though as that did seem to help quiet things down even more. We are running perfectly quite now.
As for the heat; I removed the bottom panel and installed feet to get the units off the surface. Running much cooler now. I couldn't be happier. These things sound incredible.
BTW I never realized how much noise a phone could create just by proximity to preamp tubes, even when not physically connected.
As for the heat; I removed the bottom panel and installed feet to get the units off the surface. Running much cooler now. I couldn't be happier. These things sound incredible.
BTW I never realized how much noise a phone could create just by proximity to preamp tubes, even when not physically connected.
Afterhaving built the DCPP and being totally satisfied with the quality ofthe amp, i decided to buy the pcb's first version (on the way) forthe 50w monoblocs.
The problem is that currently it is almostimpossible to buy 6hj5 tubes (I thought it would be easier up until startlooking for them). What is the best substitute for 6hj5? and what changes do I have to make?
As I am nota specialist like many of you (this will be the third tube amp that Ibuild), I ask you to have a little patience and try to detail thechanges that I must do as best you can.
Best regards
Caetano
The problem is that currently it is almostimpossible to buy 6hj5 tubes (I thought it would be easier up until startlooking for them). What is the best substitute for 6hj5? and what changes do I have to make?
As I am nota specialist like many of you (this will be the third tube amp that Ibuild), I ask you to have a little patience and try to detail thechanges that I must do as best you can.
Best regards
Caetano
Unfortunately there is no drop in substitute for the 6HJ5. The 6HD5 is the same tube with a minor pinout change. It is also rather scarce.
There were over a dozen tubes that fit the original single board DCPP amp and rather minor changes were needed to run 6HJ5's in that board. It may be possible to go the other way in the mono board. The 6HJ5 has the G1 and G2 pins reversed compared to the common sweep tubes, so the stopper resistors were crossed over to make the changes.
I have not seen Pete's mono block board, so I do know if either of these mods are easy, hard or impossible.
I have some new boards of my own design in process. They will come in sizes from wimpy to monster (500 WPC). The first prototype of a mid sized board is being populated now, so I won't have time to play with Pete's new board for a while. There will be a new thread to discuss the options with my design once I see if the first proto makes sweet sounds, or stinky smoke. This could be just a few days away depending on family issues.
I saw 250 watts per channel and 525 watts with both channels paralleled come from the original DCPP. If I remember correctly There were a couple of PC board traces that were too close for comfort at that power level, so I settled on 100 to 125 WPC with the 6HJ5's. The plate voltage swings from near zero to about 1500 volts under these conditions, and could go to twice that if the amp is ever driven to clipping into a highly reactive load like a guitar speaker near resonance. I measured 250 watts into a resistor with a nice pretty sine wave. I wouldn't want to plug my guitar in and set all the knobs to 11.
A flashover fed by a power supply capable of feeding a 500 to 1000 watt amp is ugly and eats up parts. A recent event of this magnitude destroyed a PC board and magnetized the OPT!
Resistors rated for kilovolts are not common, but series combinations can be used to satisfy the end to end voltage requirement. The end of the feedback resistor that is connected to the plate of the output tube MUST be kept away from EVERYTHING, especially ground plating on the board. I have a board with a hole burned through it to remind me. This occurred at about 160 watts of power on a 36LW6.
Again, I haven't seen the new board but the 6HJ5 IS a 6DQ5 in a Compactron bottle. 6DQ5's are available, and 26DQ5's are somewhat common, so the 50 WPC recipe Pete published, or the 125 WPC recipe that I published in the original DCPP thread should apply with these tubes in the new board.
Any of the bigger sweep tubes with a 35 watt plate dissipation rating and higher could use the same formula with a 2500 ohm OPT for more power. 2500 ohms on 650 volts with 35LR6's will make 250 watts. 4 X 36LW6's into 1250 ohms on 650 volts will make over 500 watts without glowing.
6HJ5 / 6HD5 was unique for a 24 Watt sweep tube in not having a plate cap, and using a somewhat different Compactron pinout from other sweep tubes (grid1 and grid2 flipped). Electrically it is very close to 26/6DQ5 and also to 21/6LG6. 6EX6 is also close except somewhat lower gm1 (use a -NEW- 6EW6 driver tube in place of the 6CB6 for more drive signal, pin compatible).
Unfortunately, the grid stopper resistors for grid1 and grid2 are on opposite sides of the tube sockets on this board. But could still be crossed with some insulated wire extensions on the resistors.
The bigger Compactron sweeps like 35LR6, 6LB6, 36/6KD6, 42/6KN6 have a little more gm1, so would still be easy to drive by the board, just a different base pinout. (Most have the grid1 and grid2 flipped from the 6HJ5, plus a plate cap)
The 21/6LG6 is a 28 Watt Compactron base sweep tube, electrically similar to the 6HJ5, but a different pinout, and has a plate cap. The 6V heater version is rare and expensive, the 21V version is cheap. Could use a common 24VDC regulated supply adusted down to 21V for the heater (separate wires to the isolated heater pins).
26/6DQ5 and 6EX6 are octal base with a plate cap. Can be found inexpensively. A total base re-wire needed obviously. (the new multi option board version would fit well for these)
21/6HB5A is another Compactron base tube with just 1 base pin conflict (pin 2) and no plate cap. It is only rated for 18 Watts dissipation versus the 24 Watts diss. for the 6HJ5, but has the same size plate. The 6V heater version would almost be drop in except for pin 2. Some 6/21HB5 tubes have a grid 1 cooler fin up top of the top mica, so clearly can handle more than the rated 18 Watts. (the 6HJ5 has the grid1 cooler fin and the same size plate)
35LR6 has a similar Compactron pinout to the 21LG6 and a plate cap. Its a 30 Watt tube. Higher gm.
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I don't think that there were enough of them around to interest China. 7,000+ 6HB6's, yes that's where they went after they were talked up here. 20,000 13GB5's were grabbed up by an unknown "American Buyer." This happened right as I got a 100 WPC amp running with the 13GB5, then I could not get any tubes for the amp. I tossed the PCB in the trash and started over.
The 6HJ5 and 6HD5 were never that popular to begin with. Most were made by Raytheon for an unknown purpose, possibly the sweep tube for a CRT radar set or something like that. I have never seen one in a TV set, but I didn't keep up with the TV trends after 1973. The Raytheon 6HD5 data sheet does state TV use, and it is dated 1962, so I should have seen one during my years of TV repair, 1967 to 1972.
There are some Motorola branded 6HD5's that were Japanese made. These could have been made for TV use. There is a 21HD5 and a 28HD5 in the data books, but I have never seen either of them.
When I first stuck the 6HJ5 in the big red board there were only about 400 in stock at the usual Florida tube shops. I bought 50 of them and have collected maybe 10 more at hamfests and such.
Two suffered glass shattering explosions in a recent experiment gone very wrong due to some dumb blonde arithmetic.......they don't live long at all at 200+ watts of dissipation. ....milliseconds!
The 6HJ5 and 6HD5 were never that popular to begin with. Most were made by Raytheon for an unknown purpose, possibly the sweep tube for a CRT radar set or something like that. I have never seen one in a TV set, but I didn't keep up with the TV trends after 1973. The Raytheon 6HD5 data sheet does state TV use, and it is dated 1962, so I should have seen one during my years of TV repair, 1967 to 1972.
There are some Motorola branded 6HD5's that were Japanese made. These could have been made for TV use. There is a 21HD5 and a 28HD5 in the data books, but I have never seen either of them.
When I first stuck the 6HJ5 in the big red board there were only about 400 in stock at the usual Florida tube shops. I bought 50 of them and have collected maybe 10 more at hamfests and such.
Two suffered glass shattering explosions in a recent experiment gone very wrong due to some dumb blonde arithmetic.......they don't live long at all at 200+ watts of dissipation. ....milliseconds!
Thanks very much for your help.
I will analyze your suggestions while I do not receive the pcb's but I start to think that the best hypothesis of building this amp is to order the new version and choose another alternative to 6HJ5 / 6HD5.
Any other suggestions or alternatives are most welcome.
best regards
Caetano
I will analyze your suggestions while I do not receive the pcb's but I start to think that the best hypothesis of building this amp is to order the new version and choose another alternative to 6HJ5 / 6HD5.
Any other suggestions or alternatives are most welcome.
best regards
Caetano
There seem to be some 21HJ5 tubes around, more than $3 though ($8). Just use a 24V regulated DC supply with the Vreg turned down to 21V, and separate heater wires.
With 53 Monoblock boards sold, 2 6HJ5 tubes on each, then a couple of spare tube sets for each probably, that would account for 300 tubes.
Between private stocks of 50 here, 25 there, and 50 elsewhere just mentioned, that's over 400. Although the vendors seem to find another dusty box of 100 tubes in the back warehouse occasionally. I saw a lot of 50 of them go on Ebay once, years ago, for around $2 each. Should have snapped them up I guess.
Well, 26/6DQ5, 21LG6, 21/6HB5A and 21JV6 (HB5 and JV6 have no plate cap), 21/6EX6, 6CB5A, 35LR6 should be available.
21HB5A were on the $1 lists once, so should be plentiful.
21EX6 and 21JV6 list at $3, 21LG6 lists at $4, 26DQ5, 6CB5A and 6EX6 list at $5, 21HB5A lists at $6, 21HJ5 lists at $8.
21/6LG6 were a later improved version of the 6DQ5 / 6HJ5, with lower screen current, lower heater current, and lower knee voltage. And they are pin compatible with most of the bigger sweep tubes. But have a plate cap like them.
Then there is 17/22KV6 if you want to deal with Novar tube socket availability.
Unless more 6HJ5s show up, time to get the new multi-tube monoblock PC board.
With 53 Monoblock boards sold, 2 6HJ5 tubes on each, then a couple of spare tube sets for each probably, that would account for 300 tubes.
Between private stocks of 50 here, 25 there, and 50 elsewhere just mentioned, that's over 400. Although the vendors seem to find another dusty box of 100 tubes in the back warehouse occasionally. I saw a lot of 50 of them go on Ebay once, years ago, for around $2 each. Should have snapped them up I guess.
Well, 26/6DQ5, 21LG6, 21/6HB5A and 21JV6 (HB5 and JV6 have no plate cap), 21/6EX6, 6CB5A, 35LR6 should be available.
21HB5A were on the $1 lists once, so should be plentiful.
21EX6 and 21JV6 list at $3, 21LG6 lists at $4, 26DQ5, 6CB5A and 6EX6 list at $5, 21HB5A lists at $6, 21HJ5 lists at $8.
21/6LG6 were a later improved version of the 6DQ5 / 6HJ5, with lower screen current, lower heater current, and lower knee voltage. And they are pin compatible with most of the bigger sweep tubes. But have a plate cap like them.
Then there is 17/22KV6 if you want to deal with Novar tube socket availability.
Unless more 6HJ5s show up, time to get the new multi-tube monoblock PC board.
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Wow, I figured there were more of them sitting around since they were never used in much gear or anything. I guess there just was never many made. Seemed like a pretty decent valve for the price, I'm glad I got 4 sleeves left 
EDIT: I probably have more than I need, private message me and I may part with some for a fellow DIY'er. I have 50 4P1L's to play with now
EDIT: I probably have more than I need, private message me and I may part with some for a fellow DIY'er. I have 50 4P1L's to play with now
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The reason the 6HJ5 monoblock existed was because of the modified version of the original engineers amp that I built and posted in the original thread. They used 4 tubes each. I know that I built 3 of them, gave one to my boss who immediately bought 8 spare tubes. Both of my remaining boards each have 4 tubes in them. There were about a dozen other builders of that amp that I know of, and at least a few builders who wired Pete's driver board up to 6HJ5's. These activities sucked up at least 100 tubes, probably more.
A little project that I am working on has destroyed two tubes, and presently rolling through several more, but they are all 6HD5's. That leaves me with a few more to play with, and maybe build an amp, but I don't believe that there are enough in circulation for a major project.
I think that Pete has the right idea, and the project that I am working on follows a similar concept. The supply of TV sweep tubes is dwindling, with any large stash of single type numbers vanishing over night. Any amp designed for TV sweep tubes should be adaptable for a wide range of different tubes. I have access to some of the inventory lists of a popular tube seller, and there are very few sweep tubes available in quantities of over 1000, and they tend to be small ones with odd heater voltages.
People that aren't engineer types don't even care.........they want the buzz names that go along with all the common current production audio tubes. Tube rolling is a huge thing, people love to "roll" tubes so making an amp with lots of tube choices is most of the fun for most people that purchase these amps. They are literally just toys for most people.
My favorite is probably the EL34, it's my go to valve these days for common audio finals. Lots of choices to pick from, KT77, 6CA7, and the plethora of EL34's out there including the 30 watt dissipation EL34b.
My favorite is probably the EL34, it's my go to valve these days for common audio finals. Lots of choices to pick from, KT77, 6CA7, and the plethora of EL34's out there including the 30 watt dissipation EL34b.