EF86 AUDIO PENTODE, VARIOUS TYPES & MANUFACTURERS Z729, CV2901, CV4085

Manufacturers: Brimar , GEC Valves , Mullard , Osram

The EF86  B9A based audio pentode used in many classic valve and guitar amplifiers.  On offer we have EF86 from a range of manufacturers and in configurations of single, twins (x2) and quads (x4) - remember, for those of you with amplifiers utilising  paraphrase phase splitters ala Hafler & Keros and Quad II it is ESSENTIAL to equip these with closely matched valves.

The EF86 is the standard early stage audio pre-amplifier valve. Its intrinsic design is to be low noise and anti-microphonic. The landmark amplifier designs from Mullard's application laboratories all specified the EF86, and today it is still the valve of preference for similar duties. Before the introduction of the EF86 the Mullard valve of choice for pre-amplifer stages was the EF37A - equally preceded by the EF37 and earlier the EF36.
 
Mullard described the EF86 as 'a low noise pentode intended for use as a RC coupled AF voltage amplifier, particularly suited for use in the early stages of high gain audio amplifiers, microphone pre-amplifiers and magnetic tape recorders.' 
 
When used as a normal voltage amplifier at a line voltage of 250V with an anode load of 100 k Ohms and a grid resistor of 470 k, the maximum hum level of the valve alone is 5 uV, the average value being only 3 uV when operated with one side of the heater earthed. A further reduction could be gained by centre tapping the heater to earth which results in a maximum hum level of 1.5 uV. Any greater perceived hum levels than those quoted may be attributed to the use of a valve-holder, in which excessive leakage and capacitive inter-pin coupling pins will introduce considerable hum - good quality amphenol,PTFE or ceramic B9A holders are a must!!.
 
Any LF noise generated by a valve is a function of an equivalent voltage on the control grid per unit bandwith. In the case of the EF86, for a line voltage of 250V and an anode load of 100 k, the equivalent noise voltage is approximately 2 uV for the frequency range 25-10,000 Hz.
 
Care in the design of the valve to ensure that the electrode structure and its mounting are as rigid as possible can reduce the microphony of the EF86 to an insignificant level. The structural design of the EF86 ensures no discernable internal resonances at frequencies below 1 kHz and similarly, at frequencies greater than 1kHz, the effect of vibration is usually negligible on account of the damping provided by the chassis and the valve holder.
Physical dimensions for the EF86 are as stated: - envelope of 21 mm diameter and of thin glass wall construction. Device length exclusive of base pins is 48 mm.

Some tasty exotica, past and present used the EF86 and we provide a limited list of these here:-

- 65 Amps Monterey
- Dr. Z Route 66
- Dr. Z Z-28
- Eastern Electric M520
- Matchless C-30, SC30
- Matchless DC-30
- Soundelux U99
- VOX AC30 Heritage
Bottlehead Tube Repro 2009
Brauner VM1 mic
Eastern Electic M520 amp
Lawson L47MP
Manley baby valve mic
Microtek UM92.1 mic
Neumann U47 mic
Neumann U67 mic
Quad II
Vox AC10

 

Picture of POLKA DOT CHROME MESH ANODE GEC Z729 FROM 1960
POLKA DOT CHROME MESH ANODE GEC Z729 FROM 1960
Well here's a treat, on offer is a GEC Z729, the famous pin mesh anode EF86 variant. These devices are sought not just because they look beautiful but because they also have a wonderful sound showing low microphonics and a low noise floor - some say their slightly lower gain is a problem but believe me, the the rewards for outstrip the downside by an order of magnitude. This device as you can see shows the full twin blue Osram decal, and is marked with the classic white GEC-Osram cartouche carrying the code Z729 and the sate code QD which equates to April 1960. The pins are straight and clean, the valve tests at nominal for both anode current, Ia and mutual conductance gm using our AVO Mk 4 valve tester. A simply super example of a rare high performance thermionic device.
Stock Code: Y55
Availability: 1 in stock
Delivery date: 1 week
€51.33
Picture of  GEC WHITE LABEL EF86
GEC WHITE LABEL EF86
Well here's a treat, on offer is a GEC EF86 variant. This device as you can see shows the full white "Made for GEC" decal. The pins are straight and clean, the valve tests at nominal for both anode current, Ia and mutual conductance gm using our AVO Mk 4 valve tester. A simply super example of a rare high performance thermionic device.
Stock Code: Y57
Availability: 1 in stock
Delivery date: 1 week
€27.38
Picture of GEC Z729 PIN MESH SCREEN MILITARY EF86 FROM 1950
GEC Z729 PIN MESH SCREEN MILITARY EF86 FROM 1950
Well here's a treat, on offer is a NEW miltary stock Osram Z729, the famous pin mesh screen EF86 variant. These devices are sought not just because they look beautiful but because they also have a wonderful sound showing low microphonics and a low noise floor - some say their slightly lower gain is a problem but believe me, the the rewards for outstrip the downside by an order of magnitude. This device as you can see shows the full twin blue Osram decal, and is marked with the classic white GEC-Osram cartouche carrying the code Z729 and the date code WJ which equates to September 1967. The pins are straight and clean, the valve tests at nominal for both anode current, Ia and mutual conductance gm using our AVO Mk 4 valve tester. A simply super example of a rare high performance thermionic device.
Stock Code: Y53
Availability: 1 in stock
Delivery date: 1 week
€51.33
Picture of MULLARD CV2901 MILITARY EF86
MULLARD CV2901 MILITARY EF86
Well here's a treat, on offer today is an ex equipment CV2901 the ex military high grade varuiant of the EF86. This device as you can see shows the full military cartouche in white ink and caries the factory code for Mullard Blackburn and a date code that equates to May 1963. The pins are straight and clean, the valve tests at nominal for both anode current, Ia and mutual conductance gm using our AVO Mk 4 valve tester.
Stock Code: Y58
Availability: 1 in stock
Delivery date: 1 week
€27.38
Picture of MULLARD OLD SHIELD MESH SCREEN EF86 MBLE BRUXELLES MANUFACTURE
MULLARD OLD SHIELD MESH SCREEN EF86 MBLE BRUXELLES MANUFACTURE
Well here's a treat, on offer today is an ex equipment Mullard mesh screen EF86. This device as you can see shows full white ink and caries the factory code for MBLE Bruxelles. Tested against a specification for Ia of 3mA and gm of 2.3 mA/V these devices gave the following results on my AVO VM163 valve tester: - Ia = 3.7mA and gm = 2.4 mA/V Use this data to pick yourself a matched pair or quad from the selection of singleton EF86 we have on offer.
Stock Code: y60
Availability: 1 in stock
Delivery date: 1 week
€20.53
Picture of MULLARD OLD SHIELD MESH SCREEN EF86 MBLE BRUXELLES MANUFACTURE
MULLARD OLD SHIELD MESH SCREEN EF86 MBLE BRUXELLES MANUFACTURE
Well here's a treat, on offer today is an ex equipment Mullard mesh screen EF86. This device as you can see shows full white ink and caries the factory code for MBLE Bruxelles Tested against a specification for Ia of 3mA and gm of 2.3 mA/V these devices gave the following results on my AVO VM163 valve tester: - Ia = 4.3mA and gm = 2.5 mA/V Use this data to pick yourself a matched pair or quad from the selection of singleton EF86 we have on offer.
Stock Code: y50
Availability: 1 in stock
Delivery date: 1 week
€20.53
Picture of MULLARD OLD SHIELD SOLID SCREEN EF86
MULLARD OLD SHIELD SOLID SCREEN EF86
Well here's a treat, on offer today is an ex equipment Mullard solid screen EF86. This device as you can see shows full white ink and caries the factory code for Mullard Blackburn. Tested against a specification for Ia of 3mA and gm of 2.3 mA/V these devices gave the following results on my AVO VM163 valve tester: - Ia = 4.4 mA and gm = 2.2 mA/V Use this data to pick yourself a matched pair or quad from the selection of singleton EF86 we have on offer
Stock Code: y56
Availability: 1 in stock
Delivery date: 1 week
€20.53
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