Building session at the 2007 Fest?

[PakProtector]

Hey-Hey!!!,
Any intrest in building something at the 2007 Fest? Something useful, yet simple enough to actually get done before we have to depart on Sunday? I have a few ideas...

Some suggestions...sign up, and pay for the materials. Probably a bit for some tools too. Build on Saturday, listen on Sunday...:)

The timeframe will limit the scope of the project, but it shouldn't have to restrict it too far.
cheers,
Douglas

[rca2000]

Are you speaking of a room or such, where a group of people get together, pay for a "parts kit" or such of materials(for say, a SE 6bq5 amplifier), and each of them put one together, under the supervision of a tech??

I could see how something like that would be popular. I don't know how cheapley it could be done, but it WOULD be educational, for those involved.

[PakProtector]

Are you speaking of a room or such, where a group of people get together, pay for a "parts kit" or such of materials(for say, a SE 6bq5 amplifier), and each of them put one together, under the supervision of a tech??

I could see how something like that would be popular. I don't know how cheapley it could be done, but it WOULD be educational, for those involved.

Yep, that's about the size of it. I had not thought to plan the project, but a SE amp like you described could certainly be done quite easily.

Actually, having heard the neat little amps at the Fest, a SE E-Linear 6BQ5/EL84/6Pi14 amp would be an excellent project. The most important piece will be the output Iron. The rest can be done in a small custom run from a local winder.

'pends on what students are willing to pay for such a project.
cheers,
Douglas

[Kamakiri]

I think it would be an excellent idea.

The only thing at issue is the time factor. Seems like it's hard enough to squeeze in enough time to see all the rooms let alone to get in a project that would take up an afternoon......

[PakProtector]

Hey-Hey!!!,
The time constraints are not a small issue for sure. The design would be one offering good performance right off, with room to grow.

Power supply design with maximum flexibility is just a matter of cost. The SE circuit RCA2k mentioned is a good starting point. Have to see about interest, as it's the final reason to put it on.

Spreading the DIY craft is a neat project. The Fest is an excelent venue. I thoroughly enjoyed myself looking at the stuff others had built and exploring in rooms I'd heard good things about. I think I got to them all....:)

One of the really cool things about DIY is discovering that there is nothing complicated about amp construction. No magic involved. It was a bit of a revelation for me to discover that the box with tubes sticking out of it was just a bunch of parts.

Now to the fun part, design a circuit that can be assembled quickly, and with minimum experience. Low parts count, and an intuitive circuit will be the order of the day.

Easy to drive pentodes, like the EL84 or 7591 look good at this point.
cheers,
Douglas Piccard

[WhiteSE]

I am all over that idea...Nothing like hands on experience to learn!!

[PakProtector]

I am all over that idea...Nothing like hands on experience to learn!!

So then, we have a little bit less than a year to prepare. There is much to be done.

I looked at 7591A data...at 300V B+, and a 6k a-a plate load, a pair of pentodes in Class A will make 22W. 6k6 a-a, and U-L rigging should drop that a few watts. Drive it with a LTP pair of pentodes like 12BY7 or EF184 and we're off. With a custom Heyboer power TX, there'd be the option of a negative rail for those scared of SS current regulators.

Class A takes the PS out of the equation for the most part. 400V 'lytics would be a viable option. A small inductor (~4 Hy/150 mA ) will do wonders for PS filtering. there is a limit to how far I'm willing to simplify and cut stuff out...these will be excellent amps.

The output TX leaves a whole lot of options. A very nice custom from Heyboer will be less than $80 ea. in quantity. NC-wound copies of the Peerless S-230-Q perhaps?

So, somebody who wants to try some of the prototyping will need to step up. I'm not going to be picky on this one, but I'd rather a local member. No issue if it's more than one member...

For the Fest build. Chassis plate from Front Pannel Express. Assorted hardware to attach all the Iron. Parts acquired in build-lot quantity to be distributed while underway. Tubes from any number of sources. There has got to be several sources of 7591A in JJ or EH.

To pay for it all, likely a 2.5 month lead time, up-front payment...it would make the perfect Christmas present...:)
cheers,
Douglas

[tubino]

If you wanted to go with a really inexpensive yet proven SE triode design (but low power), there's Bob Danielak's "Darling" amplifier, using 1626 tube driven by 8532. I could donate some tubes, some PS iron, ... maybe even some prepunched chassis plates. I managed to scavenge some, years ago that already have holes for a 7 pin mini, a 9 pin mini and an octal socket. I built a Darling using one plate (they are small!) per channel. You need a 12 volt supply for the 1626, but it's a tiny xformer.

Nice thing is that with such low current and watt numbers, the OPTs can be whatever you scavenge from an old Grundig, RTR, little Japanese stereo amp, whatever. You might get by just fine with PP iron too. I've heard old Fisher and Scott iron with 20ma unbalanced DC running through it, and it can work just fine. There's probably a little gap in there to help prevent saturation...

Google Bob Danielak Darling amp and you'll get the schematic. Two tubes per channel, very low parts count, great first project.

[Kegger]

All very cool stuff and I'd be up for it.

But if I had to make a choice betwen el84's and 7591's, I'd say el84's, there cheaper
and are much more available both as nos and new stock.

[PakProtector]

All very cool stuff and I'd be up for it.

But if I had to make a choice betwen el84's and 7591's, I'd say el84's, there cheaper
and are much more available both as nos and new stock.

Good points Kegger. The PS is also smaller, lighter and less expensive.

There are a few things required in order to keep my enterest:
PP topology.
Class A finals
Cnservatively-run PS iron.

I prefer pentodes over triodes for voltage amplification.
I see no need to develop any design that requires tweaky, 'spensive parts.
I'd rather not make too much of a compromise on the output Iron. <$100 each.
cheers,
Douglas

[WhiteSE]

i am all about big butted trannies...the rest can be small...:-)

[tubino]

There are a few things required in order to keep my enterest:
PP topology.
Class A finals
Cnservatively-run PS iron.


Doug, it's your idea, so you can call the shots! (and I'm with you for 2 out 3 in your list above!) I just wanted to throw out an alternative, esp. one with the KISS (Keep it Simple, Smartie!) principle. If I can just offer one other suggestion: use good tubes, but cheap tubes! With so many really great tubes cheaply available just because they are not fashionable, why not design around them? With some you can buy a lifetime supply for less than the price of a 7591.

My two cents.

[mhardy6647]

Suggestions:

Using a PCB can speed the project immensely. Setup costs for a run of PCB's is pretty low... and, believe it or not, PCB wired hi-fi can sound very good, too!

Consider a headpone amp or line-amp as a project. The former can get a lot of bang for the buck (cf. Pete Millet's low-voltage hybrid headpone amp, of which I am quite enamored -- http://www.pmillett.com/hybrid_head.htm )

[PakProtector]

Hey-Hey!!!,
There are all sorts of neat valves to try. 13EM7 for one. Two for a PP amp. really decent performance available too. I heard some this weekend at the Oswald's Mill event. It was SE...but there's plenty of instruction available for SE design.
cheers,
Douglas

[tubino]

Hey-Hey!!!,
There are all sorts of neat valves to try. 13EM7 for one. Two for a PP amp. really decent performance available too. I heard some this weekend at the Oswald's Mill event. It was SE...but there's plenty of instruction available for SE design.

I think Bottlehead's first SEX amp used 6EA7 / 6EM7... Or was it 6DN7? Anyway it was a dual dissimilar triode with one half good as a driver, the second half as a power amp, not far from the 6DN7. Doug, if you wind up offering a building class with some tubes like these, I think I can supply all the tubes needed. They aren't expensive to order, but I'm offering for free, and I can deliver for free too!

I know you prefer PP, but if you can compromise your principles just a bit :D , you can REALLY keep down the number of components AND the number of solder connections. I know to an experienced builder like you, adding a phase inverter stage with plate resistor, cathode resistor, etc. is no big deal, but first-time builders may need a lot of time just wiring and soldering PS and two stages. Even if you start with all metalwork done, you would need ALL of four hours to get a class of 4-8 folks to mount sockets and transformers and input and output jacks, switch, term strips, fuse, and then wire everything up -- and that's even if you keep it as simple as two diodes and LRL for PS, driver and output stage. To make sure everyone leaves with a completed, tested amp, I think a full day would be needed. But the cool thing about hardwiring a simple amp is that folks have a real chance not only to get it done and checked out, but they can get a real in-the-fingers knowledge of what a plate resistor does, how GROUND works in both the AC and DC circuits, how the OPT is a path for both the B+ and the audio signal etc. I would argue that the learning advantage of hardwiring (over using a PCB) is substantial for DIY amp building, and the simpler the circuit, the smaller the time advantage of a PCB. And the circuit can be explained pretty easily to beginners.

But I'm openly biased in favor of SE, so take that into account.

[PakProtector]

Hey-Hey!!!,
The trade-off between PP and SE is in the power stage. SE has to be quieter, specially if triodes are used. This would be a two stage amp, regardless of PP or SE.

There are some other neat TV combo valves that are quite inexpensive...some research is needed.

Like I laid out in the beginning, there are a few things to get settled. Interest level for one. Project topology for another. Then I'd need some local Beta folks who'd take on the first batch of builds. Ideally this group would be able to consult and assist in the actual class next year.

I'd rather do PP, but a medium-sized SE amp can be done really well in a simple fashion as well. See Pete Millett's aX write up on the E-Linear amp from about a year ago. The PDF is on his site. That one done with EL84 would be pretty sweet. Probably just as well with a 7591 or 6V6.

The bottom line is that this class would be one heck of a lot of rewarding work. In truth, it's more than I should probably bite off by myself. What I'd like are some of the rezident Masters to step up and assist in what ever capacity they'd be comfortable with.

This would be a neat meeting theme for the SE Michigan AK group to tackle together IMO.
cheers,
Douglas

[tubino]

See Pete Millett's aX write up on the E-Linear amp from about a year ago. The PDF is on his site.

VERY NICE! Here's what I like about it, in no order:

Decent power for simple SE amp
No global NFB, but uses UL tap as B+ for driver stage. How cool is that?
Power supply: high-current damper diodes! YES!
CLCLC with Smart filter cap setup: 10-40-40, and smart filter chokes: 10h 35R, 1.5H 50R (low DCR) I bet that models well in PSUD for a low-impedance supply
OD3! Bring on the glow!

I think the schematic looks very hip. Plus he's got parts lists, layout tips...LINK to schematic etc. (http://www.pmillett.com/elinear.htm)

And he's giving it all for personal use, so in my opinion you couldn't do much better than this for a group project. (lots of OTHER ways to do it, but BETTER all around?) Sure, I like triodes, but this amp would get all kinds of speakers going while keeping it pretty simple. Anything cheaper/simpler will have some real compromises in power or elsewhere. The power supply in Millett's design is more beefy than you need, but not more than you want! As Doug noted, PS is gosh-darn important in SE, and the filtering here is done RIGHT to give a lot of easy low-impedance power. Yup, it's an iron-rich diet, but you can keep cost down by buying surplus mil stuff.

[tubino]

Oh, and if youse guys want to go with 6CJ3 or similar novar dampers, I've got the sockets you want! Ceramic & silver mil-spec! These are Canadian (NOT the Russian MAGnovar sockets for EL-509 etc with bigger pins), and they are cool and hard to find. I bought a quantity years ago...

[PakProtector]

Hey-Hey!!!,
The E-Linear amp is a reasonable option. One could follow Pete's KT88 design, or one could shrink it to EL84/6V6 level, or somewhere in the middle with 7591's. It is a very useful and forgiving design, and it can be expanded into PP( my favourite ).

I do favour smaller for the first builds. A buy of James SE iron would be easy to orchestrate, and custom power could be had from Heyboer. Lots and lots ov options....:)
cheers,
Douglas

[Squidward]

Sign me up for the debugging build session. I can also take pics for an assembly manual. I also can scrounge a bunch of tubes, to help suppliment. I can especially source the OD3, and I agree: Bring on the Glow! I love that purple tube!

In my limited experience, the most time consuming and least rewrding work can be the chassis. Having a pre-punched/drilled chassis can save hours of meticulous work.

Count me in! :thmbsp:

[Strawman]

I am very interested. Had a discussion with Squid, and he seemed pretty excited about it. If it can be done on a real poor mans budget that has more time and interest than dollars, and you guys are willing to share you're knowledge, I don't see how it could be anything but a successs. Even people that can't or don't wan't to spend the money right away can get a real "inside view" of what's required to go from 0 to 100. :thmbsp:

[PakProtector]

Hey-Hey!!!,
Well then, seems that the next thing is to come to some consensus on the circuit design. The E-Linear circuit Pete laid out has some values laid out that may not apply to other variants. From the D3a and its g2 regulated voltage, to the PS design, it has been tuned for that circuit.

The power tube can also be run full-pentode, and still run the driver from the screen tap. It's just a question of load-line calculation, and driving it where it's at its best. It can run 6L6's, or EL34's or 6550's( or EL84, 6V6, 7591A, EL500 and a host of TV sweeps ). An interesting option for me would be the TV sweeps run as pentodes at moderate voltage and reasonable load. There are a few neat ones that would offer reasonable power, and cost $5-10 each.

Also it's a bit much for a weekend build. Stuff like a dropping resistor and bypass cap to the driver pentode will be both cheaper and simpler.

Remember, it's your amp. I'll be able to assist the design process, and make sugestions on the circuit. Once we've got that part down into something that looks buildable, we'll move on to parts sourcing and layout.
cheers,
Douglas

[grumpy]

I am sorry guys but while this may seem like a great idea the logistics, cost, manpower and most importantly the liability make it impossible to pull this one off.

Now if someone wanted to give a small seminar on say the basics of soldering or something like that it may be possible.

[markthefixer]

Alternately:

How long does it take to raccoon ONE wooger????

[PakProtector]

Hey-Hey!!!,
ANybody interested in building should drop me an email. I'll run a 'reply-all' mailing as we discuss the project. Those of you in SE Michigan( or withing your sane driving distance ), are welcome to visit in person to smoke-test, or troubleshoot as the project gets built. I'll be building either way....

Or open a thread in DIY....:) if the interest is there, I'll be there to make it happen.

Maybe it will even appear as a low liability thing, and a Fest Build could still happen.
Cheers.
Douglas
Pentode-at-netscape-dot-com

[luvvinvinyl]

...or build between now and next year, and show off the systems you put together, centred by the amp each of you built! That would be a cool room!

[CarlV]

I am sorry guys but while this may seem like a great idea the logistics, cost, manpower and most importantly the liability make it impossible to pull this one off.

Now if someone wanted to give a small seminar on say the basics of soldering or something like that it may be possible.
Seminars at future AK fests would be great!


Carl

[PakProtector]

Seminars at future AK fests would be great!


Carl

Now that is both interesting and useful. Say for example, taking a single triode gain stage, and examining the effects of load changes, and operating points with a signal generator and distortion analyzer. Pick a triode---any triode---and examine how to use it in circuit.

This sort of measurement would be interesting to me. If one could look up the answers, there's be no reason to actually do it...of course, engaging in experiments, in front of students, real-time, and w/o a lot of previous confirmation of the results is one slightly risky business....:)

cheers,
Douglas

[Kegger]

Hey Douglas I was thinking something along the lines of what Luvvinvinyl had to say.

As I'll have a room next year so time will be limited plus the amount of stuff to see at
the show, a building project would severely cut into the other enjoyments of the fest.

So I was thinking once a final build is determined we build it on AK/here local and show
what we've created at next years fest and have them looked over by the guru's like
yourself and others that would help to see how we did or tweak or whatever.

That way even people who can't make it to the fest could tag along with the project
and even jump in from afar with building one themselves then see what happens with
the ones built and brought to the fest.

I would jump in on this build in a form like mentioned above and would travel local to
get guidance or help in any way I could. But to really think about my next years fest
I have to be honest and would not have the time for a build at the fest.

What yu think? Also you to Tubino as I know you have extensive knowledge in this area
also and could/would maybe be able to meet somewhat locally on a get together?

[PakProtector]

Hey-Hey!!!,
I would be the greatest loser of time at the '07 Fest if the build project had gone ahead. I realized that from the start. Having it cancelled ahead of time is somewhat of a relief...:)

Anyway, like I offered, I'll put up what ever effort needs to be made to present a group build project. Tubino likes SE, and we have already found one that has his interest. My wife's 6V6 monoblock project is another simple one. That one does take a special OPTx, but getting Heyboer to clone the little Chicago would not be a great issue...I want a slilght modification to it anyway, so a takedown is in the cycle plan for that one anyway.

We've got about a year to get a simple project up and running so a finished/tweaked amp can be brought to the Fest. Just need to get moving...:)

I suggested a small mail-list for discussion, similar to how Jeff's Audio group is run. That 'Reply-All' is a powerful thing, and I can't think of a better way to do it. Aside from creating the original mailing, and adding new folks, it's a self-powered discussion as far as I see it.

I like to see the DIY craft spread, and I'll make the effort to do it. This project is just small way I can pay forward the folks who taught me.
cheers,
Douglas

[Kegger]

OK so it sounds like your in the same boat and a build at the fest would take up much of
our fest experience, (I agree YOU would be severely limited on time) so doing a build here
or through email/local is the thing to try and acomplish by next festifus and somewhat of
the preferred way of doing it!

Sounds good to me.

I have a set of fisher output's plus power from a 7591 amp and a set from a 7868 both
are integrated's that I could use the iron from and build whatever is suggested or go in
on something a group was to decide on, I'm flexable and either works for me.

I haven't done a build yet, just mods and upgrades so any build would be good from my
point of you and could definatly use the experience. I'm in for whatever is being done!

Cheers!

[tubino]

My wife's 6V6 monoblock project is another simple one. That one does take a special OPTx, but getting Heyboer to clone the little Chicago would not be a great issue...I want a slilght modification to it anyway, so a takedown is in the cycle plan for that one anyway.

Which little Chicago OPT is that? I was given a pair of cute little Chicago OPTs years ago, and when I did a cliplead trial of several different OPTs in a 1626 amp I built, the little Chicagos were my favorites. I forget the model number though...

I like 6V6s too, and happen to have a LOT of good used tested ones.

[tubino]

It can run 6L6's, or EL34's or 6550's( or EL84, 6V6, 7591A, EL500 and a host of TV sweeps ). An interesting option for me would be the TV sweeps run as pentodes at moderate voltage and reasonable load. There are a few neat ones that would offer reasonable power, and cost $5-10 each.

I'm very much attracted by using non-trendy tubes like sweep tubes. IIRC, there are some different limits that must be observed (much lower screen voltage?), but that's do-able. My very first scavenged tube amps were a pair of DuKane PA amps using 6CD6 tubes, an odd 2.5A filament tube that I think was used in some McIntosh amp too... Hate to sound like a broken record, but there are a lot of sweep tubes I could donate for a project. The big 'uns like EL-509 are kinda on the pricey side, but there are many little cousins -- and if you don't like the price, just design around the weirdo fil voltage variations! Plenty of 26 and 42 volt cheapies out there. Or in my storage unit.

[Markus111]

OK so it sounds like your in the same boat and a build at the fest would take up much of
our fest experience, (I agree YOU would be severely limited on time) so doing a build here
or through email/local is the thing to try and acomplish by next festifus and somewhat of
the preferred way of doing it!

Sounds good to me.


Sounds good to me too. If you guys are thinking of a local or email kind of thing, count me in! I just plain ran out time at the fest, but it could be fun to get together on a Saturday or something.

Mark

[Squidward]

Sounds good to me too. If you guys are thinking of a local or email kind of thing, count me in! I just plain ran out time at the fest, but it could be fun to get together on a Saturday or something.

Mark

I agree. Count me in, too!