Dating ampeg v4
A reissue of a classic model, the Ampeg V-4B is a tried-and-true 100-watt all-tube bass head.
With a design dating back to 1971, the V-4B has proved to be a reliable warhorse with a great sound ever since.
The second deals specifically with Ampeg guitar amplifiers. It's a US (possibly Japanese) 6L6-GC, sometimes with a taller bulb, with two extra pins.
The first deals with 70A (hereafter referred to as just 7027) in general.
You liked the tone, in the case of the V amps, loved the cool tone controls, in the case of the Portaflex they look way cool, too. Someone said you might use 6550's, but they weren't sure..
Fear not, gentle reader, for the kind folks at Ampeg not onlyforesaw the problem and provided a simple solution, they made your Ampeg one of the most versatile amplifiers on Earth in regards to adapting to different output tubes! You can pop in *any* good matched pair of 6L6-GC, (except skinny Chinese & Russian ones), 7581, 5881, 6L6-WGB, or KT66 without any modifications, because the socket is actually wired for 6L6's.
I've also put US made 6L6-GC of various flavors, Philips ECG 6L6-WGB, GE 7581, Sovtek EL34, Tesla EL34, Russkie & US 6550 in it successfully. I'm still a bit leery of the idea, but several folks as well as Lord Valve say they work, so I'll try to blow them up next..
Some 7027's had gold-plated grid wires, but that does not affect the actual tube ratings (other than maximum DC grid resistance, pretty much a non-issue when replacing 7027's with 6L6's) or power output...actually, the Tesla/JJ 6L6-GC has gold plated grids, too, if you're into gold plated grids.
OK: I have a Sylvania 7027, 6L6-GC, and 6L6-WGB and a GE 7027 (made by GE,not an RCA relabel) and a GE 6L6-GC.
This most recent release adds a few helpful modern features, while staying true to the legendary tone of the original.
If you open up the Ampeg V-4B, you'll find 2 x 12AX7s in the preamp section, generating the rich tonal core of your bass sound.