Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on October 07, 2010, 02:36:10 am

Title: Hammond Universal 125d OT
Post by: TIMBO on October 07, 2010, 02:36:10 am

Hi guy's. I got a 125d OT i want to use in my next build. I don't know which lugs i need for the speaker connection. I have a 4ohm speaker and as per their hook-up data the primary impedance is anywhere from 1.5k - 27k. Some help needed, Thanks

Title: Re: Hammond Universal 125d OT
Post by: mresistor on October 07, 2010, 05:45:11 am

See this chart at hammond  mfg for the 125 series  - look down the 4 ohm column (found at the top) and select the primary impedance you are going to use. Then look to the left and hook up those output wires  - for instance  if you want 5K ohm primary impedance for a 6V6 then connect the speakers to output lugs 1 and 4, which would be close enough. 
What amp are you wanting to build? Will it be PP or SE?

http://www.hammondmfg.com/125.htm (http://www.hammondmfg.com/125.htm)

hope this helps........   someone else will chime in soon....    :smiley:

Title: Re: Hammond Universal 125d OT
Post by: TIMBO on October 07, 2010, 02:29:19 pm

Thanks for the reply, My problem is that i don't know the primary impedance of a single 6L6 or how to calculate it. I understand the chart OK. The amp is a 10w class A SE. Also the say that the amp can max 15w at full noise will this OT be OK. Thanks

Title: Re: Hammond Universal 125d OT
Post by: bigdaddy on October 07, 2010, 02:39:17 pm

What's the B+ voltage of the power transformer?

That transformer is actually a push pull but can be used for a SE amp too. Honestly......go out and buy a David Allen TO11C and that would serve you best for that build.

But if you must use that tranny use the blue wire to your plate on the power tube and the brown to the first node for your rail. Use the 2&6 taps for 4200ohms primary and 8K secondary.

From experience use a dropping resistor of at least 2K and screen resistor of at least 1.5K on the 6L6GC.

Title: Re: Hammond Universal 125d OT
Post by: phsyconoodler on October 07, 2010, 06:39:16 pm

You should have used the Hammond 125DSE part number.The one you have is push-pull and will not sound very good with a single ended amp. D is 10 watt and SE is single ended.

Title: Re: Hammond Universal 125d OT
Post by: TIMBO on October 08, 2010, 04:58:50 am

OK, sounds like i've got another build on my hands :smiley:Please enlighten me to a valve combo that would give me a 10w push pull. Thanks

Title: Re: Hammond Universal 125d OT
Post by: phsyconoodler on October 08, 2010, 10:59:38 am

Fender Harvard.Nice tones. 6AT6 preamp tube.
  A Princeton with no reverb.Perfect for that OT.An 18 watt marshall with a cathodyne PI.Sweet,sweet tones with less grind.More voxy chime.Just a volume and tone control.Two EL84's for 10-12 watts.Well within the Hammond's range.
  The princeton could be done with a Raw control.Nice tones.
A Princeton Reverb/Tweed Deluxe PT and your 125D,a small tag board a couple of controls,a pair of 6V6's or EL84's and you are done.The tone will make you smile.
  All can be done cathode biased.It will sound killer good.A 5Y3 rectifier tube will keep the voltages down to a good level.

Title: Re: Hammond Universal 125d OT
Post by: TIMBO on October 08, 2010, 03:09:23 pm

Thanks for that  :wink:As i do have a couple for Mullard EL84's waiting for a home. I had them for a while so i assume they are a match pair.Is it ok if they are not? and will it have a marshall sound. And while i have your attention what lugs will i need to connect to? Thanks