speakers and cables

An external high pass filter maybe?  I bought a M&K external high pass,around 30 years ago, give or take, and I don't recall it costing an arm an leg.

Anyway, in a nutshell (if I've got this right from memory) your RCA outs from preamp will go into highpass/from high pass L & R RCA out to amp and also L&R RCA out to subwoofer.  I do not remember at what frequency mine was preset to roll the bass off to the sub.  Mine has a treble level adjustment (speakers) and bass level adjustment (sub).

Besides allowing you to use RCA cables to hook up sub, other benefits are freeing the amp up from as much bass as it was  powering before, which also frees up the speakers from trying to reproduce as much bass as they were before. 

I remember at the time immediately hearing things sound much more dynamic with the smaller stereo tube amp (Cary SLA70) I was using at the time.

I also remember a dealer basically turning up his nose at the notion of using one.  "Another crappy box," he told me.  But he didn't use the term 'crappy.'

I quit using it when I became a 'purity of signal' snob and also because I bought bigger amps and they seemed dynamic enough without it, and also because I had acquired equipment with truly balanced circuits that I wanted to use and the M&K high pass only has RCA ins and outs.

Like everything, pros and cons.  But long story short--that would probably solve the blowing fuses issue you are having.

Can't you go from the R & L amp outs to the subs and subs usually have outs for the main speakers.

@noromance

that’s what I did, as shown on pics. Should I just wire left to left, right to right as on picture #2?

@immatthewj

most everything I have is crappy (except for my TT and bookshelf speakers). Just one RCA out from preamp. I can use a splitter

no sub out from amp

I can’t buy another component, I have to make what I have work.

It’s a 45 year old amp with the tightest binding posts. (That’s why it took 90 minutes, to group and isolate naked wires in 1/20 inches of spaces.)

I can’t buy another component, I have to make what I have work.

I gotcha; I totally understand.  

But I am going to ask anyway if I am understanding this correctly:

Just one RCA out from preamp.

You are saying just one pair of RCAs (L&R) out from the preamp (going to the amp), correct?

That's what I interpreted, anyway, when you said you had no sub out in your preamp.  I understand what you were saying about not buying another component, but I'll clarify what I was saying anyway:

the highpass filter goes between the pre and the amp.  In other words, that one pair of RCAs out to the amp now goes IN to the highpass filter.  (Highpaass filter then rolls off the bass, but I am not sure at what frequency).  There are two pairs of RCA outs in the highpass filter, and the pair with the bass connects to the subs (although in my case it was sub as in singular), and then the pair with the remaining treble goes to the amp.