Amplification Impedance Question

[J3FF3R00]

Hey twid crew. I’m wondering if there’s any way for me to use my 100w tube amp (Marshall JCM900 1x12 combo) with 8 ohms impedance to power a larger bass cabinet (Ampeg 4x10 HLF) with 4 ohms impedance. 
I feel like it has to be possible in some ways. 
I also have a basic Ampeg head that I usually use to power the 4x10 cabinet but it obviously doesn’t have the tube overdrive, reverb, etc. I’m assuming it probably isn’t possible to daisy chain the Marshall combo into the Ampeg head and them into the 4x10 cab without blowing something up. 
Anyway, I’m clearly not an electrical engineer type. I just want a beefy tone and am teased by looking at my gear and wanting it to work for me. 
 

[user]

According to the JCM900 manual there should be a Direct-Out on the rear which is the pre-amp signal so that would make daisy chaining it into your Ampeg a possibility. Additionally it says that there is a Impedance Selector Switch on the back and the combo's can be set to either 4 or 8 ohms.

Generally when you want to use a speaker that has lower impedance than your amp you're ok as long as you keep the levels low, otherwise the speaker might draw too much current and the amp might overheat.

Curious to hear how this works out. My brother found a VS265 dual 65 watt combo in the trash some weeks ago and I got to spend some time fixing it. Even though I can't really play and the valvestates are probably entry-level Marshalls it sounded really great to my ears. First time hearing an amp like that in my own living room and it totally clicked.

[J3FF3R00]

Thanks for the insight!

I think the thing that threw me off on the rear panel…

… is the “impedance select” switch on the Marshall combo (jcm900 4101) says “8” in one position and “4 (16)” in the other. What is the “(16)” bit about?

I’m assuming if I plug anything into either the direct line out or the loudspeaker outs I will need to unplug the 12” combo speaker that is currently plugged in, right? 

 I’m assuming that if I were to plug my 410HLF into one of the loudspeaker outs on the combo (after switching the impedance to 4 ohms) I would just use the same speaker cable that runs between the bass amp (Ampeg B1-Re) and the 4x10 cab? 
Also, you mentioned keeping levels low but is that also necessary if I’m switching the impedance to 4?

2nd to last thing, if I’m going to try the daisy-chain route, can I plug the 410 into the direct out using a standard guitar cable?

Last thing, which of the 2 would you try first: switching down to 4ohms and plugging the 410 into the loudspeaker out or daisychaining with the direct out?

Sorry for all of the questions but I can’t tell you how many times I’ve googled this without gaining further understanding of my situation. I just don’t want to destroy my gear, obviously. I’m surprised there isn’t a YouTube video where someone tried it.

Edited July 22, 2023 by J3FF3R00