Fender Bassman 135 crackling issue

[big sender]

My Bassman has recently started crackling during practice with a band I recently joined. It's been not used much in the last 15 years except for home recording etc. I've never had this issue before. I'm assuming tubes but will be testing some other theories.
What I really want to know from the Bassman crowd out there is you set up and configuration and whether the 4 ohm push is ok into an 8 ohm speaker.
Here is what I'm running at practice, which in my 20+ years I always thought was OK.
Rickenbacker with stereo cable out of the "Rick-o-sound" jack running to both the Bass input and the Normal input, the normal has a distortion pedal on it too. Bassman from the Ext. Jack (4 ohm) into a 1x15 Ampeg 8 ohm cabinet. Crackling started during practice the other week.
Here is my home recording and general dicking around set up.
Rickenbacker stereo out to Bassman with a 2x10 and the 15 in series (16ohms) for the bass pickup and the treble pickup to a Hiwatt 50 1x12 Combo amp for top end distorted. Never had any issues and I turn up just as loud at home when the wife and kid are away.
My research has just confused me. The schematics seem to say that and other forum entries in various places that the parallel is the way to go or match the impedance on the amp
4 to 4. Even some talk of "shorting" the Ext. jack and using the Speaker jack will solve this. I always thought that you could run any combination off a 4 ohm output except any 2 ohm speakers
Does the single 8ohm speaker cause issues? Did I frak up the tubes?
Who's running a Bassman 135 and what's your advice?

Thanks!

[anderbass]

Originally Posted by big sender

Here is what I'm running at practice, which in my 20+ years I always thought was OK.

I don't know whats wrong with your amp but sounds like its probably due to go to a tech.

I'd be running those 2 cabs in parallel for a combined 4 ohm load. I believe your amp is rated at 4 ohms but with tube powered amps in general I've always followed the advice that its safer to go with a numerically lower ohm load than higher than the amps rating like you've been doing.

[BassmanPaul]

Originally Posted by big sender

I always thought that you could run any combination off a 4 ohm output except any 2 ohm speakers

While you can get away with this with a guitar amp it is never advisable with a Bass. Running a lower than ideal load is better than a higher load but a match is always best.

My opinion is that you should take the amp to a tech for some TLC.

Paul

[big sender]

Yeah, thanks guys! That was what I was begrudgingly concluding... :-/ Too bad those amps can't last forever, such as fantastic tone.
The Bassman is off to the shop as as soon as I have the funds.

So BassmanPaul and anderbass, would you run a cable from each of the 2 jacks on the back of the Bassman to each 8ohm cabinet? Sorry to be thick about it. Just want to be safer in the future.
Thanks!