Tweed Super 5F4 output Impedance Question

[frances]

Hi everyone

I'm new to the Tweed Builders Forum

I have a question about output transformer Impedance, I Finished building a Tweed Super 5F4 circuit and it works fine sounds great. The output transformer i used is a Thordarson 4 ohm secondary. after Playing around with
the volume control looking for the sweet spot i realized this amp is going
to be over kill for rehersals .I talked to a friend of mine who has an ordignal
Tweed Super and he said to use [ 1 ] speaker ie run the amp at 8ohm's
and you will find the sweet spot at a lower volume for rehersals
and when you play a job use [ 2 ] run the amp at 4ohm's .

Is there a problem running the amp this way ?

[Chuck H]

No, as long as your speakers are up to the task. You don't want to run 50 watts into a 20 watt speaker. One speaker moves less air than two. You will get a volume reduction by running one speaker instead of two. Just make sure the amps output impedance is matched to the speaker load impedance, and the speakers can handle the wattage.

Rock on

Chuck

[tubeswell]

Running the amp at double (or for that matter half) the designed OT impedance probably won't kill it, although it will alter the tone a little and give a bit more bite. (More impedance = shallower load line). So go ahead and plug your 8R speaker into your 4R socket. It will double the 'normal' load on your output tubes, and you will get a bit of reduction in volume but not much.


I build my amps with multiple secondary OT taps so I can mismatch the impedance by a 'knotch' one way or the other for different effect. In fact I ran a PV tube amp at 1/2 the design impedance for 2 and 1/2 years continuously and it didn't do any harm.

However, if you don't hook up any speaker at all, or conversely, run it at too-high an impedance (like 3 or 4 - or more- times the design impedance) you will get unwanted problems

[frances]

thanks for the info

Thank's Guy's for the input

I think I'll stay on the safe side of things and use the proper load 4ohms. I
some times use a [ Boss Blues Driver ] to shape the sound on my other Amps
at lower volumes, It's only for rehersals so i think i will do that


Thank's again Guy's

Frances

[BarryW]

8 into a 4

I had the strangest thing happen on my 5f4 build - or maybe I just have no clue about these things (a real probability!)

I wired it up to 4 ohms, ran my two speakers stock - but when I wire in just 1 8 ohm speaker outside the cabinet, it just honks/buzzes! Very strange. Any idea why it would do this?