72-74 Bassman 10

JiM · Post by **JiM** » 23 Nov 2008, 13:58

The "external speaker" at the back of you bassman is an additonnal OUTPUT, to connect more speakers to the amp.
You talked about connecting together the outputs of two amps, which is likely to blow both of them !

If you want to use the bassman as a cab, you have to disconnect the amp from the speakers. You can then connect them to any amp (as long as you match the impedance).
Meanwhile, do not switch the bassmann on without speakers (or some dummy load instead), it could fry the output transformer.

TragicTravisty · Post by **TragicTravisty** » 23 Nov 2008, 14:35

ok, so if the amp is off, but another amp is plugged in the back, it could blow the transformers?

Fuzzer · Post by **Fuzzer** » 23 Nov 2008, 18:21

Well, the audio transformer is there to adapt the output of the amplifier to the speakers which is a low impedance (4, 8, 16 ohms); if you connect that output to an amp's input (1M) you can cause serious damage to the transformer.

For what I can tell, you want to take a cable out from the active amp's output and plug it into the inactive amp's external output, to which normal output is a cab connected.

But that doesn't make any sense, so, I guess I haven't understood yet.

TragicTravisty · Post by **TragicTravisty** » 24 Nov 2008, 14:02

im not plugging an amp into another amp, im connecting two amps (one of which is off) to the same speakers

TragicTravisty · Post by **TragicTravisty** » 17 Dec 2008, 12:20

looking at the preamp of the tweed bassman, there are a few main differences. the biggest one is that there are 3 gain stages(2 on silverface), the only difference between the two channels is a treble bleed on the bright channel. also, the tubes are biased to 800,800,100, where in the silverface they are all 1500. with the tonestack, they are both fairly similar, although the tweed tonestack is after the gain stages. the tweed bassman (at least the schematic i was working off) actually has a blackface type tonestack...

main question is whats the difference with the biases?

moltenmetalburn · Post by **moltenmetalburn** » 17 Dec 2008, 16:34

TragicTravisty wrote:im not plugging an amp into another amp, im connecting two amps (one of which is off) to the same speakers

That may be your intention BUT the external speaker jack on your amp is an OUTPUT ONLY never an INPUT as previously answered here:

JiM wrote:The "external speaker" at the back of you bassman is an additonnal OUTPUT, to connect more speakers to the amp.
You talked about connecting together the outputs of two amps, which is likely to blow both of them !

If you want to use the bassman as a cab, you have to disconnect the amp from the speakers. You can then connect them to any amp (as long as you match the impedance).
Meanwhile, do not switch the bassmann on without speakers (or some dummy load instead), it could fry the output transformer.

You can connect another cabinet to the bassman but not another amp!

Ronsonic · Post by **Ronsonic** » 17 Dec 2008, 17:26

TragicTravisty wrote:im not plugging an amp into another amp, im connecting two amps (one of which is off) to the same speakers

Well, you sorta are plugging the output of the live amp into the output of the cold amp in parallel with the speaker.

Please, just don't do it. Nothing good will come of it.

dave_b · Post by **dave_b** » 17 Dec 2008, 21:44

TragicTravisty wrote:why?

Because the speaker out jack is an extra output for the amp, not an input for the speakers.

TragicTravisty · Post by **TragicTravisty** » 17 Dec 2008, 23:43

i dont intend on doing it any time soon, and im not trying to be a dick, so we can just drop this if you want, but i am aware that it is an input. my question is what can it harm?

TragicTravisty · Post by **TragicTravisty** » 17 Dec 2008, 23:59

but anyway, what does the hot biasing of the tubes do in the tweed bassman?

also, for the tonestack in the tweed, i assume that being post-gain basically makes frequency compression set by the guitar pickups, and boosts frequencys, while in the silverface, the tonestack can compress some frequencies more than others? (with dirt, obviously) although in the silverface, theres very little clipping at all, so i guess it doesnt matter...

Ronsonic · Post by **Ronsonic** » 19 Dec 2008, 19:34

TragicTravisty wrote:i dont intend on doing it any time soon, and im not trying to be a dick, so we can just drop this if you want, but i am aware that it is an input. my question is what can it harm?

BLOW THE FUCKING SHIT OUT OF ONE OR BOTH OF THE AMPS!!!!!!!

The amp that is on will have the load of the other amp's output transformer secondary in parallel with the speakers. We cannot predict what this load will be. Well we could but it will take a page of equations that I'm not going to do for the purpose of justifying simple good advice. In short the primary will be an unloaded coil of about 1 ohm resistance and little effective inductance connected to a very large coil that is going to rise and collapse a field that will be fed back into the active amp's output at some phase off from the input. So, the active amp sees a near short with a bunch of out of phase voltage, more or less equal to what it is putting out coming back at it. That reflected signal will go straight through the NFB loop where it will get injected into the signal path forming a feedback loop of parts from two different amps that nobody has ever connected together before. If you're lucky it will just sound really bad.

The amp that is off will have an AC voltage applied to the secondary that will be fed directly to the NFB circuit and will have a much higher induced AC voltage applied to the secondary and from there to the plates of the power tubes and whatever else is connected there. This is relatively (relatively) benign compared to what is happening in the live amp but unpredictable since nobody has deliberately tested this or again, bothered to calculate the damage.

True, most tube amps are pretty rugged and you may be able to get to a power switch some time between noticing that something is horribly wrong and something being destroyed. hell, it's your amps.

A really good mod for the Bassman Ten for guitar is to plug the ports in the cab. Just pull a speak, reach in and use some RTV to glue blocks of wood over the ports. The tuning is way better for guitar. Mine has the PPIMV mod and one channel is wired up like a Super reverb, without the reverb. Nice.

Ronsonic · Post by **Ronsonic** » 19 Dec 2008, 19:40

Oh, why not just make a cable with a female 1/4" on one end and a male on the other. I keep several, at home, in the shop and in the gig bag. Really handy when you need to get into a combo cab for some reason.

TragicTravisty · Post by **TragicTravisty** » 19 Dec 2008, 23:52

thanks for explaining this to me. what era super reverb did you mod it for?

Ronsonic · Post by **Ronsonic** » 20 Dec 2008, 01:36

I just pulled an old blackface schem. Don't even quite recall - was a few years ago. The main thing was the tone stack - this was not a fussy recreation of any sort. Just a pretty simple rewire and some component changes as I recall.

Oh, sorry, for shouting. It slips out once in awhile.