*****contest****contest****contest****

[dhuebert]

The prize will go to the person who can build the smallest stereo power amp.

Some rules before we begin:

1: Must use a transformer or switching style power supply. No using mains like AA5 radio.

2: Must use 7 or 9 pin miniatures, can use octals if you like.

3: Torroids OK.

4: Must have volume pot

5: Any more ideas for rules?

Judges and prizes TBA

Don

Don

[Ty_Bower]

Any restrictions on gain, or power output?

Need it be capable of driving "normal" 4~8 ohm speakers, or can we use some bizarre multi-hundred ohm drivers and skip the output transformers?

Is "smallest" defined by weight, volume, or footprint?

[kheper]

The prize will go to the person who can build the smallest stereo power amp.

Some rules before we begin:

1: Must use a transformer or switching style power supply. No using mains like AA5 radio.

2: Must use 7 or 9 pin miniatures, can use octals if you like.

3: Torroids OK.

4: Must have volume pot

5: Any more ideas for rules?

Judges and prizes TBA

Don

Don

The amp must do greater than 1 w/ch or your entry will be rejected.

RCA input jacks only. No mini or sub-mini jacks permitted.

5 way binding posts required.

All tube components, except for rectifiers, bias and css.

Compactrons. Nuvistors, etc. permitted???

Vertical mounting of tubes only.

[EWBrown]

Well, I guess that kills off my idea of a "Porsche engine" PP amp with horizontally mounted tubes coming out the sides Yellow_Light_Colorz_PDT_09 Yellow_Light_Colorz_PDT_05 Yellow_Light_Colorz_PDT_04

I can design, but, as my parts and supplies are about a thousand miles away, I'll be a late entry... Yellow_Light_Colorz_PDT_02

Extra Credit for using really "weird" oddball tubes.

/ed B

[dhuebert]

The amp must do greater than 1 w/ch or your entry will be rejected.

I think I can see what you're going for here but measurement is a problem. Now we have to get into standards etc. I would like to keep this as loose as possible.

Well, I guess that kills off my idea of a "Porsche engine" PP amp with horizontally mounted tubes coming out the sides

Do it. Marks for originality for sure. This will be peoples choice, so we'll have a poll to determine winner. Since it can take a couple of months to get parts and time together, we might have to make it a spring (?) deadline.

I would be against really oddball stuff, 7 or 9 pin tubes only but if the concensus is otherwise then I'm in.

6: There is no rule number six

7: All schematics must be posted in order to win.

8: Size will be determined by the volume of the smallest shipping container it can fit into.

9: Combination IEC power connector and fuse OK

10: Any banana plug output OK

11: RCA input

I would like to see normal 4 - 16 ohm output to keep the amp flexible.

Also bonus points for an iPod docking station.

Don

[Ty_Bower]

Is this going to turn into a spud contest, or will multi-stage/multi-tube amps be weighted favorably in the scoring?

[TomMcNally]

Does it have to be stereo ?

Weight might be a good way to judge too.

[SDS-PAGE]

This is getting interesting. Love to see what you guys come up with. Maybe after this one, we could go to the other extreme and come up a contest wherein the biggest amp wins. -Min

BTW, what will be the prize? Just curious.

[dhuebert]

multi-stage/multi-tube amps be weighted favorably in the scoring?

If you can build one that is smaller than just a power amp then sure.

Does it have to be stereo ?

Yes.

what will be the prize?

I was hoping this could be a cooperative kind of venture with participants donating prizes. Since these amps are likely to be single ended, I will donate a Get Set Go board to the prize cache.

To review:

1: Must use a transformer or switching style power supply. No using mains like AA5 radio.

2: Must use 7 or 9 pin miniatures, can use octals if you like.

3: Torroids OK.

4: Must have volume pot

5: Must be stereo

6: There is no rule number six

7: All schematics must be posted in order to win.

8: Size will be determined by the volume of the smallest shipping container it can fit into.

9: Combination IEC power connector and fuse OK

10: Any banana plug output OK

11: RCA input

Don

[kheper]

multi-stage/multi-tube amps be weighted favorably in the scoring?

If you can build one that is smaller than just a power amp then sure.

Does it have to be stereo ?

Yes.

what will be the prize?

I was hoping this could be a cooperative kind of venture with participants donating prizes. Since these amps are likely to be single ended, I will donate a Get Set Go board to the prize cache.

To review:

1: Must use a transformer or switching style power supply. No using mains like AA5 radio.

2: Must use 7 or 9 pin miniatures, can use octals if you like.

3: Torroids OK.

4: Must have volume pot

5: Must be stereo

6: There is no rule number six

7: All schematics must be posted in order to win.

8: Size will be determined by the volume of the smallest shipping container it can fit into.

9: Combination IEC power connector and fuse OK

10: Any banana plug output OK

11: RCA input

Don

10 is questionable. If binding posts are just "ok", no-one will use them. They will use those stupid strips to cut down on the overall dimensions.

9 and 10 should be mandatory for a modern amp.

[dhuebert]

If binding posts are just "ok", no-one will use them.

I didn't say anything about binding posts, just banana plugs.

Don

[TomMcNally]

I didn't say anything about binding posts, just banana plugs.

Please clarify that ... a "banana plug" is a MALE ... do you want
males hanging off on wires - or banana JACKS which are females ???

Yellow_Light_Colorz_PDT_08

[EWBrown]

Since it would be several months before I could actually put the darn thing together, I'll just toss my ideas up for grabs: :o Yellow_Light_Colorz_PDT_11

13EM7 or 13FD7 SET stereo (tried, trued and tested)

13FD7 is a 13EM7 crammed into a "fat bottle" 9 pin miniature.
These are normally dirt cheap, I've gotten them for less than a buck apiece. Yellow_Light_Colorz_PDT_06

These tubes have a "sweet spot" of V P-K of around 230V, and IP of around 38 mA. I found this combination from extensive testing and experimenting. It works...

Triode 5W "Fender" SE OPTs. (small and low cost)

Fender 4H, 90 mA, 110 ohm DCR choke. good physical match to the OPTs.

Trafomatic 250-0002 toroid power trannie (perfect match for the 13EM7/13FD7, I've used several of these over the years).
The 13V filaments are run in series, and on AC, and yes, I made them totally hum-free. The HV secondary, under approx 78 mA load is 211VAC,
and this delivers the right B+ voltage for the best operation of these tubes.

Basic "spud amp" circuit:

VA: RA= 100 to 120K, RK = 1K, VA B+ = 240VDC, IP = approx 1.1 mA

PA: RK = 820 ohms, 5W; B+ = 260-262VDC. IP = 36-38 mA.

I've built two other similar amps, but using fancier output iron and larger chassis, so I know this works and sounds good. Output is 2 to 2.5W RMS.

The smaller "big amp" fits neatly onto a 6X10X2 inch Hammond chassis, and uses James 6113HS OPTs, Trafomatic 250-0002 PT and the aforementioned 4H, 90 mA, 110 ohm DCR "fender" choke. The larger "big amp" is on a 12X10X2 chassis, and uses MQ BCP-15s and EX045s. Parallel feed, and a definite overkill, right down to the 24 position stepped ladder attenuator. Wretched excess, but well worth the effort and expense. PeeWee Amp won't be so grandiose, but it can be small and "cute"... Yellow_Light_Colorz_PDT_16

FWB rectifier , using 4X uf4007, two 100 uF / 450V caps, drop to 240V for the VA through a 10K resistor, and 22 uF, 450V cap.

RCA inputs, 100K "rat shack" stereo volume control (or better) and the usual 5-way binding posts.

With the smaller output iron, this could be crammed into, and onto, a much smaller chassis than 10X6 inches. I'm thinking cast "Bud Box"...

Perhaps something like this one: (previously posted by "Hot Sauce" )



THough it would need a somewhat larger cast aluminum bud box, to fit the Trafomatic Toroid and everything else inside...

GO for it! Yellow_Light_Colorz_PDT_06 Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_08 Yellow_Light_Colorz_PDT_11

/ed B

[TomMcNally]

Thanks for the design Ed ! Yellow_Light_Colorz_PDT_16

[EWBrown]

Go 4 it!

I have all the parts, and actually started putting it together, but now everything is a thousand miles away, and I won't be seeing them for another 5-6 months :o THe Bud Box I have is somewhat larger than that... Yellow_Light_Colorz_PDT_04

The trafomatic "donut" is the biggest item, may be tricky to cramm it all inside Yellow_Light_Colorz_PDT_11 :o THe original purpose of the trafomatic was to power four 16A8s, with DC filaments, and I'm sure that Boris Sasic had no idea about applying it to 13EM7s, for which it is a match made in "heaven".

I figure tubes, OPTs and choke on top, and the rest of the :guts" packed inside... I/Os and vol control TBD by the builder Yellow_Light_Colorz_PDT_11


The other "small amp" I built a while ago was the "gizmos" 6T9 into a 6X9X4 two piece bud box that cost me a buck at a flea. It definitely has that "soviet cold war military surplus" look to it, only the tubes are on top, everything else is inside. that kicks out around 4 WPC, and sounds OK, but the 13EM7 / 13FD7 SETs sound better...


/ed B