Dagnall D2507 help

[angelodp]

Hi, I have a Dagnall D2507 OT transformer.

I worked out the TR and its a bit puzzling.

Primary is Brown, Red, White

Sec is Grey, Yellow, Orange, green

Grey to Y - 35.1 TR
Grey to Gr - 24.1 TR
Grey to Or - 9.7 TR

This was done by injecting AC from the primary side until i got 1 v AC on the sec side at each pair and then did the TR calc.

When I do the rest of the math

35.1 sq= 1232.01 x 4 ohms = 4928 looks good for 2 EL34's
24.1 sq = 580.81 x 8 ohms = 4648 still good for the 2 EL34's
9.7 sq = 94.09 but even the x 16 = 1504 does not look like I can get a 16 ohm tap

What is that connection for if not another tap??

Hope this is clear enough.

[martin manning]

http://www.etronic-parts.com/product_in ... CM800.html

Orange is common. Are you sure it's good? Your grey-orange connection should look like a 16 ohm secondary.

[Stevem]

How much voltage where you pumping in on the primary side for the 1 volt output?

[Phil_S]

+1 on Stevem's question. I use a filament transformer, putting about 7V on the secondary, resulting in 100-200+V range on the primary. I believe the bigger numbers will give you a more accurate calculation.

OTOH, if Martin is right about the orange, then you've got to re-figure the whole thing. It is certainly worth trying the assumption that orange and not grey is the common. That still doesn't explain the orange-grey combination. Any possibility it is a screen tap?

Another possibility is that you've got an internal short. This is the test for it: http://www.premierguitar.com/articles/t ... r-tester-1

[martin manning]

How much voltage where you pumping in on the primary side for the 1 volt output?

Should be exactly what is listed as TR above.

[angelodp]

Thanks guys, I'll rework the orange as common and see, that may just be the trick. I put in just enough voltage to get 1v on the sec side in each instance so the ratio shows the voltage input.

Best A

[angelodp]

Ok a little error on my part

I now used R - W for the prim ( bwn was center tap )

Using Or as common

Or- Gr = 13.8:1 TR sq = 190.44

Or- Gn = 20:1 TR sq = 400

Or- Y = 28:1 TR sq = 784

Set up as a table below

Or-Y ** Or- Gn ** Or- Gr ** spkr ohms

28:1 * 20:1 * 13.8:1

1568 - 800 - 380.88 --- 2
3136 - 1600- 761.76--- 4
6272 - 3200- 1523.52--- 8
12544- 6400- 3047.06 --- 16


I was expecting that my numbers would work out for 2 EL34's in PP
since I believe this OT came out of a Marshall. But it looks like the target
value that matches for 4 8 and 16 ohms is around 3.1- 3.2k
My Tube manual shows an ELR ( P to P ) of 6500 for 2 EL34's

Not sure what this OT is best suited for ??
Any thoughts or help.

Ange

[martin manning]

This OT is from a JCM800 1987X reissue amp. I'm guessing someone upgraded to a boutique OT in pursuit of better tone, and sold this one off. 50W Marshalls with 2x EL34 typically use 3k2-3k4 primary impedance so you are getting just what is expected.

[angelodp]

Thanks Martin, how does that square with the info listed in the tube manual?

Best Ange

[martin manning]

Thanks Martin, how does that square with the info listed in the tube manual?

There are a lot of variables involved in choosing a load line... Plate and screen voltages, UL or not, fixed or cathode bias, and whether you want maximum output power, or minimum distortion. FWIW, Mullard's EL34 data sheet shows 3k5 for 400V Va fixed bias, and 6k5 for 450V cathode bias. TW Express runs 6k6 at 400V fixed bias.

[angelodp]

Martin, thanks for the clarification.

best A