Best Harp Amp I've EVER heard.....

[jrfrond]

Without a doubt, the best harp amp I've ever heard was a Premier Twin 8 that one of my customers brings in here every so often for routine maintenance. It's basically a Champ-type circuit with a S-E 7591A power section, and in order to sound RIGHT, a NOS 7591A must be used, because the replacements just neuter the amp totally. Over the years, I've kept this amp going by repairing solder connections, noisy resistors, replaced the speakers (w/Jensens), cleaned pots, replaced jack. The usual. But I have NEVER heard an amp sound like this for harp! Sounds pretty nice for guitar too. Real Rev. Billy tones, with a smooth high-end response. The amp is built SO cheaply, and I think this is what gives it the vibe. I've offered the customer lots of $$$ for the amp over the years, but no dice, he will NOT part with it, and I wouldn't either!

[loudthud]

I must assume you have never seen another one. Do you have a schematic? There was one on ebay that ended today. Seller is in Hawaii ~

Found a hand drawn schematic online at

http://www.harpamps.com/premier/schematics.html

The schematic specifys a 6L6 output. Could be more than one version.

[stratavox]

Look over at Schematic Heaven; iirc, there are 5 versions, some with a 6l6, the rest using the 7591. The Model 50 is essentially the T8 minus the trem. I built one (with help from several folks here and elsewhere), and like it a lot, using a new 7591, a Hammond 275-0-275 P/T, diode recto, and two surplus Randall 8's...ymmv...

[loudthud]

I'm tempted to build one because I have some NOS 7591's. But I'm curious, what makes people dislike the re-issue 7591's. Is the transconductance too low? Do they just not have enough gain? Are there any mods that could be done to the circuit to make it work better with the re-issues?

[R.G.]

Re-issue 7591s are down-bottled 5881s, unless some tube factory has really stretched things in the last year or so. The transconductance is half or less of real 7591s.

The 7591 is unique, a super-gain 6v6 sized tube with 6L6 power handling. It was one of the last tubes designed new, along with the 8046(?). These were intended to replace the 6L6 in hifi applications; the 7591 with the same power at smaller size, the 8046(?) with more power and higher current (= lower ratio in the OT and better frequency response) for higher end amps.

[Bruce Saunders]

Vero Amps stopped using 7591's because of microphonics, both new production and NOS.
http://www.veroamps.com/news.html

I built a twin 8 clone, but I really didn't care for the tone controls, far too interactive for my taste.

[TheTinMan]

The Twin 8 and the Premier 76 both appear to have no cathode resistor on the first triode stage. I've never seen that in a guitar amp - what's it doing?

Thanks,

Chip

[MWJB]

These amps are "grid leak" biased, very common in the early 50's (see 5C? Fenders). From the mid 50's onwards cathode biased preamps became the norm.

Works better with some types of mic than others, can struggle when hit with a big signal.

[jrfrond]

Right on about the new 7591's. Just rebottled/repinned tubes. Sounds AWFUL in the old Premier. Not enough drive to push the output into saturation, so it's just this crunchy mess, and NOT in a good way!

I've seen the 6L6 versions of this amp. Not nearly as dynamite. Of course I can clone it, but I know it won't have the same mojo. Most cloned vintage amps almost never do.

[Bruce / Mission Amps]

I've been building a harp amp clone version of this amp for many years using a KT66 and cathode biased preamp tube.
For the lower power player and a decent PA, it can't be beat and sounds even better with a single 12" to me.

[arnenym]

Maybe a little OT..?
Anybody tried EL 34 's?

[stingray_65]

Started looking at those hand drawn schematics and had to clean them up a bit.


Fair warning I've not built this and I have a few discrepensies that are noted on the schematic but all seems in order.