Miscellaneous Rumbles

Any ideas what this Marconi Valve is for?

1

Been sorting out an old box of broken lead wires, rusty guitar strings. Hiding in the bottom I found a small oblong red and grey cardboard box with the legend

Marconi (Trade mark of the Marconiphone co. ltd.) Valve written on the four longer sides.

On one end that opens is printed Marconi EF86/Z729 Then B.V.A. (or maybe 8.V.A.) in a circle

13/6 P.T. EXTRA

13/6 is UK predecimal currency thirteen shillings and six pence......£0.68p in todays decimal . PT is Purchase tax..the fore runner to VAT.

The other end only says Marconi but the inside flap says 17 MB- 560

The valve itself looks brand new!

Any ideas what it is for ?

2

Some Vox amps had the EF86 in a preamp spot.

Great sounding, but many have stated that the EF86 was prone to being micro phonic in this preamp spot.

Nice find BTW.

4

thanks for info J(ust an old Cowboy)D

I have never had a vox amp. Burns sonic 50 combo transistor amp traded for a Simms Watts 70w then to a Fender Bandmaster stack then a Fender 75 combo

I used to use watkins copicat echos (still have 2) wondered if it could have been a spare for one of those

5

Thanks GG wiki gives a good description of valve characteristics and uses but no specific guitar amp usage or echo chambers.

6

EF86 tubes are pentodes as compared to half a 12AX7 which is a triode. They have a huge bloom which triodes do not. If you've never played an amp with this preamp, do yourself a favor.

You can also design an EF86 preamp using the Blencoe book as a guide. Less microphonic tendency than the Denney design, but also less gain.

7

The Matchless DC30 is very much based on the AC30 and the second channel uses an EF86. The Dr Z Rt 66 and KT45 use one too. New production EF86s tend to sound bad and are prone to rattle, so NOS is the way to go.

A lot of players rave about the EF86 but it's never really done anything for me.

8

My two Winfield amps use an EF86. I have no experience with this preamp in any other amp but they sound wonderful in the Cyclone and Typhoon. That sounds like a nice tube you have there!

9

EF86 tubes are pentodes as compared to half a 12AX7 which is a triode. They have a huge bloom which triodes do not. If you've never played an amp with this preamp, do yourself a favor.

I've had a 1960 AC30/4, a replica AC30/4 I built, and a replica AC15 (the same circuit, just lower power). Bloom is a good way to put it. They all shared that characteristic. Notes just get really big and 3D. They're not like any other amp I've owned.

And as others have said, they seem to have been primarily used in British amps and now British-inspired amps. I know they were also used in a lot of hi-fi and other audio gear, but I'm not sure if that was again primarily a British thing or not. I think not.

10

Seems first generation British guitar amps were all built with radio hi-fi bits and pieces. My Quad ll's use EF86 preamps. I think Dick Denney must have purposely over tweaked the EF86 to make it growl like that. Otherwise you need to follow it with a triode stage to get the same kind of gain.

11

Powdog, many early amps were designed and built using radio parts and circuitry. The designers (Leo Fender, for one) just copied schematics out of the Sylvania Tube Manual. Every radio has an amp in it, and the technology for guitar amps was in it's infancy.

12

Oh absolutely. I was primarily referring to the EF86 as a preamp choice. Commonly used in hi-if, it didn't take long til Vox found out that the vibration from bigger amps uncovered it weaknesses. I have a box full of EF86's that ring like an alarm clock in Vox circuits.


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