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Old 9th March 2011, 08:39 PM   #1
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Default design & build 300w ot & pt

I need to figure out a 300w pt and ot for a bass amp, and Im wanting to match specs of the 300w trannies on the webber website that they no longer stock. Im new at this, but I've got my rdh 4 book and a few others that Im starting to read. If anyone can give any advice on how to wind this thing I would be very grateful

here is the links for the two trannies:

https://taweber.powweb.com/store/wpt300sch.jpg
https://taweber.powweb.com/store/ot300sch.jpg

Yes, I do have permission from them to build these. Unfortunately, these two links is all the info they have, Ted was the one who designed these and this is the only documentation on them he created
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Old 10th March 2011, 02:36 AM   #2
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The kit which includes the wpt300 has 6 off KT88 output tubes.
That is 3 pairs in push pull parallel.

For 1 pair of KT88 (see Duncan Amps webpages for data sheets)
EITHER
B+ = 550V, either Ultralinear connected or fixed +300V on the screens, Raa = 4500 Ohms for 100Watts out (2.5% distortion in pentode mode or 2% in Ultralinear).
OR
B+ =450V and Raa= 4000 Ohms for 70 Watts

That kit only claimed to put out 200W which suggested that they are running the KT88s at a the more conservative B+ of 450V (for 70 Watts per pair).

I would just buy an off the shelf Hammond 1650W (280 Watts 30Hz to 30 kHz, Raa = 1900 Ohms). The 280W rating is not a problem because you will not be driving it down to 30Hz. It will do 300W bass amp no problem.

For 300W Bass Amp with durabilty I would suggest the 1650W output tranny with 4 pairs of KT88. At B+ of 450V ideal Raa would than be 4000/4 = 1000 Ohms. Since the Hammond is 1900 Ohms you would want to hook a 4 Ohm Speaker to the 8 Ohm tap to reflect a 950 Ohm load.

Use PSUDII Power Supply simulator (also from Duncan Amps pages) to work out what power tranny you need for a B+ of 450 Volts.

Hope this helps a bit.

Cheers,
Ian
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Old 10th March 2011, 03:49 AM   #3
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Im not sure if I'll have room for four pairs of kt-88's... yes I'm going to build the ab200, I'll just figure out how to mod that layout to run two extra kt-88's
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Old 13th September 2012, 05:01 PM   #4
palmas is offline palmas  Portugal
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Quote:
Originally Posted by coreythompsonhm View Post
I need to figure out a 300w pt and ot for a bass amp, and Im wanting to match specs of the 300w trannies on the webber website that they no longer stock. Im new at this, but I've got my rdh 4 book and a few others that Im starting to read. If anyone can give any advice on how to wind this thing I would be very grateful

here is the links for the two trannies:

https://taweber.powweb.com/store/wpt300sch.jpg
https://taweber.powweb.com/store/ot300sch.jpg

Yes, I do have permission from them to build these. Unfortunately, these two links is all the info they have, Ted was the one who designed these and this is the only documentation on them he created
The power transformer can be easily wired for you, the output TR, try this:

http://www.lundahl.se/pdf/1693.pdf

you can have 360W with 1K:4Ohm
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Old 13th September 2012, 11:50 PM   #5
AJT is offline AJT  Philippines
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Quote:
Originally Posted by coreythompsonhm View Post
I need to figure out a 300w pt and ot for a bass amp, and Im wanting to match specs of the 300w trannies on the webber website that they no longer stock. Im new at this, but I've got my rdh 4 book and a few others that Im starting to read. If anyone can give any advice on how to wind this thing I would be very grateful

here is the links for the two trannies:

https://taweber.powweb.com/store/wpt300sch.jpg
https://taweber.powweb.com/store/ot300sch.jpg

Yes, I do have permission from them to build these. Unfortunately, these two links is all the info they have, Ted was the one who designed these and this is the only documentation on them he created
to build this OPT, you will need M19 core, 1 3/4 in center leg stacked to 2 1/2 inches......

this is my go to site: education+diy

output-trans-winding.html
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Old 14th September 2012, 12:34 AM   #6
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Is this a "bass amp" for hifi or a "bass amp" for bass guitar?

One possibility, which simplifies the project greatly is to build either a paralleled amp OR a bridged amp.

The parallel amp will have more current capability and lower DF, while the bridged amp will have much more voltage swing capability, and therefore more "power". These broad statements depend on the specifics of the design... especially the target output impedance.

In the case of the parallel design, one would use two identical output stages, usually with the secondaries of each output transformer in parallel. A series connection is possible.

The bridged design puts the grounds of two identical output stages together, and puts the load between the secondaries "hot" lead.

The advantage of both of these is that one can build an amp with higher power while using components that are nominally of "lower power". For example one could use PP 6550 or KT88 tubes per output transformer - and not need exotic or oversized iron.

One also no longer has to worry much about matching, bias points and importantly runaway tubes or flat tubes hogging, sharing or loading... as compared to a quad or sextet of parallel tubes on a primary.

The larger the iron, the harder it is to get really wide bandwidth, or put another way it gets more expensive and more critical in terms of the design and winding methods.

Just a thought...

_-_-bear
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Last edited by bear; 14th September 2012 at 12:38 AM.
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Old 14th September 2012, 02:06 AM   #7
kevinkr is offline kevinkr  United States
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Since this is based on a Webber bass amp kit I've moved this thread to Instruments and Amps for the following reason:
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Tubes / Valves All about our sweet vacuum tubes Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum
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Instruments and Amps Everything that makes music, Especially including instrument amps.
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Old 2nd October 2012, 05:23 PM   #8
Struth is offline Struth  Canada
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Hi Guys

If you are building a a 200W output, then just use the Hammond 1650T , a quad of 6550/KT-88 and a 600V supply. The latter you can generate from off-the-shelf toroids in a stacked arrangement: two pieces of Hammond 182M117 or 182K240.

Each of the toroids should have its won bridge and 400V cap and bleeder resistor. One supply is tied to ground and the other stacked on top. This will give you about 320V for screens. You can also use this for the preamp B+.

This is the basis for the 'Major' project in TUT5, which puts out 200W.

If you want to use all-classic iron, then you could use the 1650T and 278CX to have 160W with a quad of any large-bottle tubes. This is the basis of the 'Custom Special' project in TUT3.

There is absolutely no advantage to winding your own transformers. Lamination suppliers want to sell their wares by the kilogram not by ones and twos. The off-the-shelf parts above are available world wide and have proper insulation for beyond the expected duty.

The Hammond 1650W is 28-lbs! It is a major piece of iron that will produce 450W for instrument use using six 6550s and a 700V supply. It is a direct but not drop-in replacement for the Fender PS-300 if you want normalised output connections.

If you want to see what is involved in designing a big output stage, see 'The 400' chapter in TUT6. Various tube types are used as a starting point to achieve 400W output, to see what the compromises are for each type; 6L6, EL-34, KT-77/88, 6550, EL-509 (real), JJ EL-509S (octal), 811A are looked at.

Have fun
Kevin O'Connor
londonpower.com
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Old 2nd October 2012, 08:53 PM   #9
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Quote:
Originally Posted by bear View Post
In the case of the parallel design, one would use two identical output stages, usually with the secondaries of each output transformer in parallel.
_-_-bear
Thanks! I had been asking about just that, putting the secondaries (outputs) in parallel. It seems to me easier to get better perofrmance and more packaging possibilities from multiple small OTs. Without such complicated winding schemes. And the push & pull sides will match more exactly.

Weber still has that big bass amp kit in their catalog. Are you saying they can't deliver the parts, or the whole kit isn't really available? With the inter-stage transformer like an SVT it seems interesting, but will that simeple preamp SOUND like a complicated SVT? Or what do you plan to use for the preamp, coreythompsonhm? Real SVTs are too darn expensive, and I don't know the quality of their parts.
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Old 2nd October 2012, 08:54 PM   #10
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Quote:
Originally Posted by bear View Post
In the case of the parallel design, one would use two identical output stages, usually with the secondaries of each output transformer in parallel.
_-_-bear
Thanks! I had been asking about just that, putting the secondaries (outputs) in parallel. It seems to me easier to get better performance and more packaging possibilities from multiple small OTs. Without such complicated winding schemes. And the push & pull sides will match more exactly. I was afraid of some ringing or other problems from minor dissimilarities.

Weber still has that big bass amp kit in their catalog. Are you saying they can't deliver the parts, or the whole kit isn't really available? With the inter-stage transformer like an SVT it seems interesting, but will that simeple preamp SOUND like a complicated SVT? Or what do you plan to use for the preamp, coreythompsonhm? Real SVTs are too darn expensive, and I don't know the quality of their parts. Weber kits seem like decent value for the money, if you like putting them together (which I do). Just the opportunity to chromeplate or powder coat some parts makes it seem worthwhile LOL.
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