845 output transformers
Raymond Koonce
I need some transformer advice before I act. I ordered a pair of potted
SE output transformers supposedly optimized for the 845 output tube.
6.5K to 4, 8 and 16 ohm, 30 watt rating, air gapped for 20Hy
inductance. The transformers came today, and they're much smaller than
what I expected, weight about 6 pounds, in cans about 3.5 inches square
and 4 inches tall. Does this sound right, or are these things going to
melt as soon as I hook 'em up to a KV? BTW, the price was right.
The 845 project is a new amp-building experience for me, so the advice
of someone who's done it would be appreciated. I'd like to get this
right without wasting a lot of $$$$ on parts I won't use otherwise.
Patrick?
TIA and best regards,
Raymond
Patrick Turner
Raymond Koonce wrote:
6 lbs is 2.7 Kg.
That sounds too light for an OPT but it depends what power you want.
My 22 watt SEUL OPTs are about 4.7Kg, and the 36
watt OPT for 4 x EL34 or 3 x 6550 are about 5.5 Kg, and about the same
weight at the power tranny. And I use really top grade GOSS for both.
What you have may be quite OK depending on the power you want
to actullay use.
I like to get the iron weight up, so I can easily achieve the
primary inductance required with a gapped core, without having to use
too many primary turns, resulting in a full power bandwidth from 15 Hz to 65
kHz, at least, before NFB is applied.
I like the AC power losses to be less than 6% .
Saturation behaviour is also OK, ie, when you crank it to full power, and
roll the F down to 10 Hz, you don't get these vicious current spikes.
SE always requires the tranny to be as big as your wallet can afford.
Patrick Turner.
Jansoe
Single-Ended or Push-Pull. You may get some ideas in
http://www.sowter.co.uk/ or http://www.audionote.co.uk/index_comp.htm .
Actually, buying a commercial product available from these site is much more
reliable than from some "unknown" manufacturer though their price is a bit
expensive but you can get a quality payback.
"Raymond Koonce" <rko...@tyler.net> wrote in message
news:3EA48071...@tyler.net...
Invalved
Indeed I have the Sowters and they have Sowter size Q.
These are 20 lbs transformers. The ones you got are way too small. You won't
have any lows or with saturated core and a lot of distortion.
Send them back!
Johan Maessen
"Jansoe" <jans...@hotmail.com> wrote in message
news:b83tp7$9s...@imsp212.netvigator.com...
James R Doyle
: 6.5K to 4, 8 and 16 ohm, 30 watt rating, air gapped for 20Hy
: what I expected, weight about 6 pounds, in cans about 3.5 inches square
6 lbs is kinda light for a single ended transformer. Generally you fight
the competing effects of a big core for high inductance while trying to
keep the capacitances down.
You can run an 845 with a 6.5K load, but you're not going to get
alot of power. You could draw a load line for this guy with
600V on the plate... Its unusual that anyone bothered making a
transformer for 'low-power' 845. Almost every 845 OPT I've looked
at is expressly designed to take advantage of every bit of power you
can get out of this tube. That is 1kV on the plate, a 10K load and
about 20W output power. Most people dont use the 845 in the 5W
arena, unless you are a freak like me.
I use the Hammond 1628SE. 5K load. Weighs in at 11lbs. Its a fun
transformer to own since it has so many interesting possibilities
for use. Plus, if you blow it up - you're not out a whole lot of $$$.
You should do some tests on your transformer at low current with another
tube and see if you got what you think you have.
: The 845 project is a new amp-building experience for me, so the advice
: of someone who's done it would be appreciated. I'd like to get this
The 845 is not a tube for beginners... One the one hand, the voltages
often used are simply not appropriate for people without working and
safety skills. On the other hand, making the 845's grid move like it
needs to is also beyond the scope of most beginners.
-- Jim
Raymond Koonce
Thanks for your input. I had pretty much decided to send them back. I
also thought about keeping them for a 45 amp. I think they might work
well there with 1.5 watts out. I just don't think they're capable of 25
watts. I'm comparing them with the Hammond iron which I have used
several times before and they're about 1/2 the size.
Regards,
Raymond
Raymond Koonce
Thanks for the input. I thought 6lbs was too light as well. I also use
the Hammond iron (1627SE) for 2A3s and 300Bs with great results. Those
11 pounders sound good to me. I used the 1628SE with 45s :-)
Since you seem to have some experience with the 845, do you have a
schematic to share? I'm pondering a triode input, 6SN7 probably, with a
300B as a driver for the 845. I plan to run the 845 at about 1KV and
50-60mA. I have the major parts except for output transformers. I
think I'll probably go with Electra-Print iron. I bought the 6 pounders
for some tests before I spring for the bigger bux for the good
transformers, but I don't think I have what I need.
Best regards,
Raymond
James R Doyle
: Since you seem to have some experience with the 845, do you have a
: 300B as a driver for the 845. I plan to run the 845 at about 1KV and
: 50-60mA. I have the major parts except for output transformers. I
: think I'll probably go with Electra-Print iron. I bought the 6 pounders
: for some tests before I spring for the bigger bux for the good
: transformers, but I don't think I have what I need.
Well 6SN7 -> 300B -> 845 you have some great options. The Lundahl LL1677
is expressly suited for a 300B driving an 845. Its a 1:2 interstage.
Bias up the 300B at 80mA. You'll get 400V of swing on the secondary.
Rock and roll. :) These guys are $76/each through Kevin at K&K.
(www.kandkaudio.com)
For driving the 300B grids, you have alot of nice options... 6SL7.
6C45. :) WE417A/5842. ;)
Were I to do a high voltage design, this is the one I'd go after:
http://www.audiodesignguide.com/my/845se.html
I'd modify this to use the LL1677. You could also couple the 300B
and the input driver with an interstage (LL1660) and drive it in
high gain - a 5842 and the 1660 wired up as a 1:2.225 interstage.
I am a big fan of Lundahl stuff... I've got a pair of LL1660 interstages.
They are sweet! And loads of options for using them too.
-- Jim
Bob Hedberg
I won a pair of these about 11 months on ebay, as the price was really
right for 10k xformers.. It took just under 90 days to get them. I
remember this because I was threatening neg feedback if they didn't
show up soon, as I was approaching the 90 day limit for feedback. I
put them away after a cursory resistance check.
After your observations, I checked them, and they weigh in at 11 lbs
each, with aprox 34:1 ratio at 60 cycle on the 8 ohm tap. I believe
this roughly translates to 9.2 k. at 8 ohms. I haven't done a
thorough check yet.
You may have gotten the wrong model. Yours don't sound anything like
the ones I got. These are heavy transformers, and not in cans, but
the standard EI vertical lams with bell ends. Painted speckled grey
(and looking very nice).
.
I did notice the 600 v wire on the primary leads. Now I'm a bit
worried. They are supposed to be able to handle hv.
Thanks for the heads up on that.
I guess I'll find out eventually, when I get to them.
I hope this helps
Bob Hedberg
Raymond Koonce <rko...@tyler.net> wrote:
Bob H.
Just grab that plate in one hand, the chassis in the other,
and FEEL the power of tube audio!!!
(not literally, of course, just kidding. DON'T DO THAT!)
Raymond Koonce
I don't think we're talking about the same transformers here. I bought
mine from the manufacturer on special order. He doesn't sell on ebay to
my knowledge. He does make replacement guitar amp transformers; perhaps
this is the reason for the small core size.
Best regards,
Raymond
Bob Hedberg
These were made by Lucas-at-large, called handwoundtransformers.com
I thought I noticed Lucas mentioned somewhere in these threads.
My xformers do have 600v primary leads, though. Guess I'll have to
get some sheathing.
good luck
N. Thornton
hI
I think i know the problem. In SE amps you have dc in the core, and
that reduces the inductance. So you need to have your 20H _at so much
dc current_. A TF with 20H with no dc will not do nearly so well when
you apply dc.
Regards, NT
Raymond Koonce
were very flattering. If this is the same David Lucas who sold
electrostatic speaker kits, I'd stay away from him.
Raymond
Paolo
Power output 28 watt. http://spazioinwind.libero.it/audiotubes/211845.htm
Ciao.
"Raymond Koonce" <rko...@tyler.net> ha scritto nel messaggio
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Raymond Koonce
(probably) transformer coupled to 845. I'm aiming for about 20-22
watts. What is the output transformer you used?
Raymond