This will document my build of Pete Millett’s DCPP “Engineer’s Amplifier”.
I have 2 Antek 230v toroids to use for B+, and series boost at the output tube plates. I’d like to have this boost on a switch, but biasing might not work out that way.
There’s another small Antek for the bias supply.
I have Edcor CXPP 100 watt 3.3k output transformers.
Currently have 6HJ5 output tubes, but really want something taller with a plate cap - this is purely for aesthetic reasons, but that is important as this thing will sit in my living room. Very open to suggestions on tube choice. The transformers are quite large, and I would like to put covers over them, which will make them look even larger, and the tubes will look a little sparse and small next to these.
Is it ok to stack the toroids like this? They’ll be under a cover and secured properly.
I have 2 Antek 230v toroids to use for B+, and series boost at the output tube plates. I’d like to have this boost on a switch, but biasing might not work out that way.
There’s another small Antek for the bias supply.
I have Edcor CXPP 100 watt 3.3k output transformers.
Currently have 6HJ5 output tubes, but really want something taller with a plate cap - this is purely for aesthetic reasons, but that is important as this thing will sit in my living room. Very open to suggestions on tube choice. The transformers are quite large, and I would like to put covers over them, which will make them look even larger, and the tubes will look a little sparse and small next to these.
Is it ok to stack the toroids like this? They’ll be under a cover and secured properly.
I stack toroids all the time. Mostly in solid state stuff, but no reason it won’t work here. Use one of the rubber discs between them.
Those Raytheon 6HJ5’s have pretty nice build quality. A similar taller octal is the 6DQ5, but you may have trouble getting them. I scrounged all the 26V version I could, before switching the new design in progress to the 6HJ5. Every single one of the 39 on hand is the Raytheon variety, although the boxes are labeled everything from GE to Philips. 6LG6 will push a little more current, but they are NOT as pretty and build quality is all over the map. Matching up octets (or even quads) to have the same innards will be harder. And I can only find the 21V version. Then of course are the 30+ watt tubes but they get pricey and wont just drop in without lowering Vg2.
Those Raytheon 6HJ5’s have pretty nice build quality. A similar taller octal is the 6DQ5, but you may have trouble getting them. I scrounged all the 26V version I could, before switching the new design in progress to the 6HJ5. Every single one of the 39 on hand is the Raytheon variety, although the boxes are labeled everything from GE to Philips. 6LG6 will push a little more current, but they are NOT as pretty and build quality is all over the map. Matching up octets (or even quads) to have the same innards will be harder. And I can only find the 21V version. Then of course are the 30+ watt tubes but they get pricey and wont just drop in without lowering Vg2.
Yes, you can stack toroids, especially in a line-level amp. Might be easier to put one on top and one underneath the top-plate, then a standard Antek cover will suffice. Get the cheaper one with the nut on top, then you can use an extra-long bolt to secure both transformers.
In theory, it looks like any of the bigger tubes with a 12FY pinout will plug right into the board, without having to hack the sockets. 6JS6, 6LR6, & 6LB6 which has a 12GJ pinout. Unfortunately, they are $30-$40 tubes, unless you can get pulls.
jeff
The 6HJ5 and 6HD5 tubes work fine at power levels up to and beyond 100 WPC. They do require some minor reversible mods in the way parts are inserted into the board in order to work. They are not a drop in replacement.
The 12FY tubes will generally drop right into the big red board without issue. As I found out with flaming results, some of the odd heater voltage variants of the 12FY tubes may have an undocumented heater mid tap on pin 7. Pin 7 is the plate pin in Petes 18 watt version of the board. My high powered version ran over 600 volts of B+ which appears on pin 7. Dropping a quad of 35LR6s into the board put 600 volts into the heater circuit making life short and unhappy for some small parts. Oddly no tubes were damaged.
See post #425 and 438 in the original thread for details.
The 12FY tubes will generally drop right into the big red board without issue. As I found out with flaming results, some of the odd heater voltage variants of the 12FY tubes may have an undocumented heater mid tap on pin 7. Pin 7 is the plate pin in Petes 18 watt version of the board. My high powered version ran over 600 volts of B+ which appears on pin 7. Dropping a quad of 35LR6s into the board put 600 volts into the heater circuit making life short and unhappy for some small parts. Oddly no tubes were damaged.
See post #425 and 438 in the original thread for details.
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Enjoy the build!
I built my version of the Engineers Amp last winter and love it! Looking at it in my living room now.
I built my version of the Engineers Amp last winter and love it! Looking at it in my living room now.
Appreciate the tips. I was really set on the 6HJ5 when I started, but now seeing the size of everything, just looking at options. I may end up using them.
I hadn't considered that. Thanks.
I was surprised at how much they're going for now that I've started looking again. It's been quite a while since I got the 6HJ5s
I'm holding off soldering the sockets to the board for now. May drop the board low so I can fit some chassis mount sockets for a different wiring scheme/socket type.
Let's see, all this fun started almost 15 years ago. For 4 or 5 years I did just about everything to the Big Red board that could be done. At one time I had three of them. The original was built with all the parts on one side since I always intended it for experimental use only. I got two more boards from Pete which were intended to be built into complete amps. I stuffed both of them with all the parts that I had in stock at the time and eventually completed an amp on a top plate, but never made the wood box for it. About this time (late 2013) I was notified that my 41 year engineering career was done and I would be leaving Motorola in early 2014. The nearly complete amp wound up belonging to my boss. The partially populated board and the well work experiment board would wind up in a moving box full of "stuff" where they would sleep for years.
After moving twice for a total of 1200 miles, boxes slowly started getting unpacked. Many just went on a shelf. This thread brought back a memory of a long sleeping box with something red sticking out of it. Could it be???? Yes, it is. It's been 10 years since I have powered one of these up. The other has never been finished.
Time to blow up some more stuff?
After moving twice for a total of 1200 miles, boxes slowly started getting unpacked. Many just went on a shelf. This thread brought back a memory of a long sleeping box with something red sticking out of it. Could it be???? Yes, it is. It's been 10 years since I have powered one of these up. The other has never been finished.
Time to blow up some more stuff?
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Yes please! Ha. It was your (and several others) experiments with this board that sold me on it back in 2016 when I was choosing a project. I ended up moving just as I bought the first few parts, and never ended up putting anything together. I now have everything needed to make the amp, and hopefully some time to actually build it.
Small update today. I was shopping for transformer covers, as I love the look of potted transformers. They were pretty expensive, and I was not sure on how well my toroids would fit (wanted all matching cubes). I found these metal Kleenex box covers on Amazon for far cheaper, and I think I’ll just flatten the top lip, and put a nice riveted brass plaque in the middle of them. They are JUST big enough to fit the toroids, and maybe 10mm to spare on the OPTs. The tube boxes shown represent where 4 motor run caps will be placed.
I’m also trying to order some 6LR6 tubes. Can’t find info on the top cap size. Anyone know off hand?
Also, I know this will make more power than my 100W Edcors are rated for, but I should be fine with just normal loud music, right?
I’m also trying to order some 6LR6 tubes. Can’t find info on the top cap size. Anyone know off hand?
Also, I know this will make more power than my 100W Edcors are rated for, but I should be fine with just normal loud music, right?
3/8”. They call it the “small cap”, but they make one smaller. And one larger. Look for the “Type 807 cap” and it will be the one that fits all the bigger (24W+) sweep tubes like the ones on the right.
Low frequency distortion will increase above 100 watts. Classic rock and hip hop have different requirements. Where the lion’s share of the power is up a bit from the bottom octave you can get away with more. You can handle more power at 40 Hz than at 20 and even more at 80. Allowable voltage at F without distortion scales linearly. You could probably push well over 200W through it as a guitar amp limited to 82 Hz. Eventually you run up against voltage breakdown issues or continuous current capacity, but should be ok with anything sane.
Low frequency distortion will increase above 100 watts. Classic rock and hip hop have different requirements. Where the lion’s share of the power is up a bit from the bottom octave you can get away with more. You can handle more power at 40 Hz than at 20 and even more at 80. Allowable voltage at F without distortion scales linearly. You could probably push well over 200W through it as a guitar amp limited to 82 Hz. Eventually you run up against voltage breakdown issues or continuous current capacity, but should be ok with anything sane.
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Thanks Ski. The 6LR6s didn’t work out (no set of 4 available), so I’m going octal. Ordered a NOS set of 6 (2 spares should be good) 6LW6s, some chassis mount octal sockets, and some plate caps.
Hi. I'll be interested in this thread because I'm building one too. I'm sticking with the 6HJ5s because they don't have a top cap. Driver tubes are 6EJ7s. The amp will be stereo (yes, it's big and heavy). I designed my own PCBs and the transformers are all from Toroidy. Your thread so that's enough.
6LW6’s (or any 30W+ 6.3V sweep tube) can get pricey - the off-voltage versions are usually a lot less.
In the 18-26 watt range the either the 6.3V or 21/26/31V series heater types could be the less expensive. Seen it go both ways recently. The 6HJ5 is still pretty reasonable - I paid $12. And you would think that no top cap would command a premium but so far no.
In the 18-26 watt range the either the 6.3V or 21/26/31V series heater types could be the less expensive. Seen it go both ways recently. The 6HJ5 is still pretty reasonable - I paid $12. And you would think that no top cap would command a premium but so far no.
6HJ5's went from $4 to over $10 when we started building 100 WPC red boards. The 6HD5 is the same tube and is still cheap if you can find them. I believe that there is a minor difference in the pinout, but they are interchangeable in the modified red board. As with the 6HJ5 almost all of them are Raytheon made regardless of the brand on the glass. There were some Japanese made tubes though. I have seen one Japanese made 6HJ5 and a few Japanese 6HD5's, mostly Motorola branded. All of my 21HD5's were Japanese. Both the US and Japanese tubes work, but don't mix them in the same amp.
The 6LW6 got pricey, often over $30 each. The 26 and 36LW6's can be found cheaper, but if you are going odd voltage octal with a plate cap use the 26HU5. They have the same guts as the skinny 'LW6's and bias up about the same. A pair will make 150 watts on 625 volts without breaking a sweat. I have pushed them to 250 watts per pair, but they were rather warm. When Stan was still around they were $12 each. I haven't looked lately. I power them with a 24 volt SMPS from Amazon turned up to 25 volts.
The 6LW6 got pricey, often over $30 each. The 26 and 36LW6's can be found cheaper, but if you are going odd voltage octal with a plate cap use the 26HU5. They have the same guts as the skinny 'LW6's and bias up about the same. A pair will make 150 watts on 625 volts without breaking a sweat. I have pushed them to 250 watts per pair, but they were rather warm. When Stan was still around they were $12 each. I haven't looked lately. I power them with a 24 volt SMPS from Amazon turned up to 25 volts.
I am building one also as we speak. I am also designing a chassis plate(s) that will be made by SendCutSend. The more I order the cheaper it gets. If anyone is interested in these possible, PM me.
Found a somewhat good deal on some 6LW6s. They're on the way now.
I'd take you up on this if my chassis layout wasn't going to be so unique. Octal sockets, sideways mounted board, moved power supply, motor run caps and a few other things. Plus I have this thing in my garage I built that should knock out an 1/8" aluminum plate pretty handily.
The 6HD5’s appear to be gone. They we’re still listed as cheap so I tried about 3 months ago but no more stock. Off-voltage LW6’s are still $18-20, as opposed to $65 for the 6 volt. *HJ5’s holding steady at $12, although I did buy the last ones RES had earlier this year. All Raytheon type, but every label under the sun. They may have gotten more since, but Dale told me the big batch of all-Raytheon-boxed 6HJ5s they started out with is gone, so it will be onsey-twoseys for a while at least as they trickle in. Most of them probably ended up in this particular build. Vacuumtubesinc (the other FL vendor) probably still has some as they‘restill listed in stock and told me they still have some 26LW6. Bought 6 more of the skinny type as insurance against any batch of 12 being bad or incomplete when I go to build the big one. I’ve got what I critically need of both types, but if I run into any more of the fat GE type I’d pick up another 6 of those.
If you're designing for Pete's original stock build, post your offer in the main DCPP thread. You may get some takers.
jeff
Many of the common sweep tubes have gotten stupid expensive. There are still a few oddities around. As vacuum tube manufacturing was winding down all of the big tube makers were involved in envelope stuffing to varying degrees. The best known example of this was the "6A3" and the "6B4" DHT tubes containing triode wired 6AV5 ( an indirectly heated TV sweep tube) guts made by Sylvania to fulfill government contracts. Sometimes other lesser known sweep tubes have "bigger than expected" guts.
For several years VacuumTubes.Net had the 25DN6 tube on their quantity specials list for 35 cents to $1 each depending on how many you buy. I bought a bunch of tubes from them one day when I still lived in Florida and shipping was cheap, so I got 100 25DN6's for $50. On paper the 15 watt plate looks like a meltdown waiting to happen, but I figured they would be good for some fun experiments. I was quite surprised when I got them. There were about 10 golden oldies that looked like they were melting just because my power supply was turned on, but there were at least 85 tubes like these. All will make 100 WPC in the red board. I have no idea what these tubes really are, but my guess would be a 25CD6. I only have two 6DN6's and they are easily meltable. These 25DN6's are my go-to medium sized sweep tubes for experiments that could end badly like the early UNSET testing.
Note that I got these 10 to 15 years ago. I have no idea what you would get today, or what another vendor would have. They are still $3 at VT.net and $2.75 at surplussales.com
The $4 to $5 17DQ6 is good for nearly 100 WPC and the $3 to $4 17AV5GA is good for 80 WPC. Those of us who have been here for a long time may remember what I did with 6AV5GA's. Note that the 6AV5GT is NOT the same tube. It melts at 40 WPC.
For several years VacuumTubes.Net had the 25DN6 tube on their quantity specials list for 35 cents to $1 each depending on how many you buy. I bought a bunch of tubes from them one day when I still lived in Florida and shipping was cheap, so I got 100 25DN6's for $50. On paper the 15 watt plate looks like a meltdown waiting to happen, but I figured they would be good for some fun experiments. I was quite surprised when I got them. There were about 10 golden oldies that looked like they were melting just because my power supply was turned on, but there were at least 85 tubes like these. All will make 100 WPC in the red board. I have no idea what these tubes really are, but my guess would be a 25CD6. I only have two 6DN6's and they are easily meltable. These 25DN6's are my go-to medium sized sweep tubes for experiments that could end badly like the early UNSET testing.
Note that I got these 10 to 15 years ago. I have no idea what you would get today, or what another vendor would have. They are still $3 at VT.net and $2.75 at surplussales.com
The $4 to $5 17DQ6 is good for nearly 100 WPC and the $3 to $4 17AV5GA is good for 80 WPC. Those of us who have been here for a long time may remember what I did with 6AV5GA's. Note that the 6AV5GT is NOT the same tube. It melts at 40 WPC.
