6V6 / 6SL7 / 5Y3GT SE Amp

[TomMcNally]

Brik -

I may have mentioned this in an old post, but the Z-mount
transformer is what turned me on to the Dremel. I had
gotten a nice kit as a Christmas gift and never really used it.

Shannon and some of the guys on here suggested it to
make a hole for the Z-mount and it's been my favorite tool
ever since. I haven't tried it for a small rocker switch,
but it's also great for cleaning up holes with burrs, and
cutting just about anything.

[Brik]

I haven't tried it for a small rocker switch,
but it's also great for cleaning up holes with burrs, and
cutting just about anything.

When a cutting wheel wears out to about 1/2" in diameter, I save it for the "rocker switch cut-out" duty.
Sometimes my choice for the power switch for an upcoming build is influenced by how many worn-out cutting wheels I have left.

[TomMcNally]

Yeah that's true, a small wheel is useful for small holes.
The Gyros wheels last a long time on steel, but wear down
quickly on aluminum. I made a 4" cut through some soft
but thick aluminum today on the bottom of my Budgie box
and wore a wheel down pretty fast.

[msmpe]

I got a hold of a bunch of hole punches (Greenlee?) that make short work of socket holes in aluminum. For EIC I again use a hole punch twice then grind out the remainder with my Dremel and a cutter bit - goes pretty quick even in steel. For anything bigger - trannies - its drill the corners and grunt my way along with a cutting disc - I don't know if a nibbler would be any quicker.

Even though it takes awhile, I like chassis work - working the metal plate, the wood formers, sanding polishing and finishing, although I'm not at all talented like some of you guys! Then when I see one of Tom's black powder coated Hammond chassis, I always ask Jeez that looks so much easier and cetainly ALOT quicker.

[msmpe]

Hi Tom,

So, let me re-cap the main changes to the schematic you made:
Rvd for the VA is 10-12K, was shown as 1.5K;
Rk for the 6V6 is 470 or 510, was 270;
Rfb OK as shown at 470K, but 560 works also.

I have a 6V6 SE in the breadboard chassis, and want to try the PtP FB. My VA is a 5751 but can't recall at what voltage, B+ is 310 same as yours, no FB, and triode strapped. I liked the sound of mine, classic SET. Lotsa bass with my big speakers, but not much more than a watt if that. I didn't try pentode mode, but would definitely try UL if I had a UL tranny to try.

[casouza]

Tom, I believe there is a misunderstanding or a typo regarding the 6SL7 plate resistors.
The plate resistor for a grounded cathode class A circuit is usually 2 to 5 times the internal resistance of the tube (rp), for minimum distortion.
120K or 120,000 ohms sems to be a good staring point, since rp of a 6SL7 is on average 44000 ohms, according to the data sheet..
12K will fry your tube.
I hope this helps.
best wishes
casouza

[TomMcNally]

Yep, the plate resistor is 120K ... see the schematic in the
first post of this thread. The 1.2K resistor they had the typo
in was built with a 12K ... I caught that right away.

[EWBrown]

I finally got myself a Dremel 200 last week, at the Wal Mart in Franklin NC. Now I have to find a local store which has the Gyros cutting wheels / bits.

It's already come in very handy for a few projects, but those little Dremel abrasive cutting wheels don't last too long - I got an extra set of 20 more, they should last me until I find some Gyros...

/ed B

[TomMcNally]

Quoting myself from July 4, 2007:

Forget about the lousy Dremel brand cutoff discs ...

look for Gyros brand - http://www.gyrostools.com

# 11-32156 and grab their mandrel model # 80-1800

I use the Dremel tool mostly for cutting IEC Power connector holes in
Hammond steel chassis, and the Gyros last forever, and I've never
had one shatter like the Dremel brand.

Ace Hardware has them, and I have two extra packs, because
they last forever.

*******************************************************

BTW ... I hate working with aluminum, it's so messy. I needed to
cut a DIN sized hole for a Kenwood car radio in an aluminum rack
panel a week or so ago, so I used the trusty Dremel and Gyros
wheel ... after the first 4" of the hole the smelly aluminum dust
was flying and the Dremel got hot and smoked and then flamed
out. Damn! I checked their web site and they said maximum
repair price for the 400XPR was $ 40 and $ 3 shipping so I sent
it in. A few days later a box came with a new model 4000, a
free tool, and a pen. Not a pen with a Dremel logo or anything,
just a plain black Papermate stick pen. Hmmm ... oh - I see,
there was a survey to fill out, they certainly got a good review
from me. Just now, I googled the 400XPR to make sure I got
the model number right, and apparently I'm not the only one
who smoked one!

quote:"My XPR 400 just burnt up as well - lots of smoke followed quickly by a short burst of flames."

Anyway - they didn't ask for a receipt or date or anything,
so they a thumbs up from me.

[Quad]

The Mandrel code is 80-18100 (small typo in Tom's post above).
I found it convenient to just get a ProPak kit, esp since
I am not in the US -

http://www.mytoolstore.com/gyros/propak.html

http://www.amazon.com/FIBER-DISK-TM-PRO ... B000N41U84

[nyazzip]

....do those Gyros come with tzatziki sauce?
i love Dremel's "EZ Lock" mandrel system for wheels, no more screwing around with mini screwdrivers and mini screws to mount a wheel, goes on and off with no tools in an instant
http://www.dremel.com/en-us/Attachments ... ?pid=EZ456

[VictoriaGuy]

As any one tried Tomiko OPT from Japan?

Ebay seller 2930luo in Canada has some. Prices are like Edcors.

Thanks in advance!

Randy

I made the mistake of ordering a pair of Tomikos from the seller you mention.
They are definitely not in the same category as the Edcors, or even the inexpensive OT10SE transformers from musicalpowersupplies.
My advice: Stay away!
http://www.diyaudio.com/forums/parts/192564-transformer-opinions-needed-size-matters.html

[EWBrown]

I have a couple of no-name Chinese made SE OPTs which make the Tomiko's look like giants, by comparison. These have a primary tapped for 7K and 5K, and 4 & 8 ohms secondary. Their power rating is expressed as "5VA" and not "5 Watts". I also have a similar set of these OPTs, of "10VA", which are still smaller then the Tomiko's

I originaly got them for the "micro-amp" build-off a few years ago, but I never went anywhere further with that design

I wouldn't try to run anything close to 150 mA through the Tomiko's, that is probably the primary's ignition current rating, at which it will suddenly burst into flames.

They may be OK with a watt or two output power, and 12B4A SE with 245 V B+ and 25-27 mA current (use a 1K, 2W cathode resistor, bypassed with 100 uF / 50VDC cap) and that should work within reason. for non critical purposes. I'd SWAG that the primary inductance is really low, 5H or less...

/ed B

[VictoriaGuy]

I'd SWAG that the primary inductance is really low, 5H or less...

/ed B

Thanks for the application idea, Ed- I appreciate it. Another project to add to the list!
About the inductance:
Your comment inspired me to pull out my BK875 inductance meter and take a few readings on the 5k winding of several different OTs I have here.
Tomiko 21H
Musicalpowersupplies OT10SE (a guitar transformer) 11H
Transcendar OT 37H
So I'm thinking 'more is better...'
Then, James 6113HS measures at 14H

Is there 'rhyme or reason' to this?

And, of course the meter isn't pumping any power through the primary.
John

[EWBrown]

The Tomiko measures at 21 H , that seems high for a cheapo small trannie It actually may be a better trannie than I would have guessed... For LF response, the higher the inductance, the better the bass There are other considerations, which mostly affect the higherfreq reaponse and efficiency, ie, interleaved windings and other "fancy" techniques". I wouldn't summarily dismiss them as being junkers, just yet...

Best thing to do is to try them out, and give 'em a listen. Using a lower current through the primary (like the 12B4A 25-27 mA) should also help out - I've used some really small SE OPTs removed from 1950's era German tube table radios, these generally are 11K: 4 ohms or 12K:4 ohms, and were designed to use with the EL95, which is a small power pentode. These work very wel with low plate currents (18-25 mA) and deliver surprisingly good sound for a small "cheap" OPT.

What test frequency (s) are you using? From my testing, I've found that a lower freq (my HP LCZ meter has 100 Hz minimum) generally gives a higher inductance reading, and as the freq increeases, the displayed inductance goes down, and usually between 2 and 3 KHz, the readings get very "squirrely" as the core hysterisis gets in the way.

FWIW, the Musical Power Supplies OT10SE works very well with a 6L6GC or 5881, in a souped up "Champ" guitar amp circuit.

/ed B