Half an ECC83/12AX7

[jay_oldstuff]

Hi chaps, off the top of your heads does anyone know of a valve that is equivalent to half an ECC83, so just one triode in the valve envelope.

Jay

[Restoration73]

I have seen a EC92 used - it's a B7G base

[G8HQP Dave]

Half an ECC83 is a 6AV6 - also known as EBC91? Just connect the two diode anodes to the cathode, and then ignore them. EC92 is quite different - is that half an ECC81?

An EBC90/6AT6 is half a 5751 - similar to ECC83 but mu=70 instead of 100.

[Radio Wrangler]

You can always use a real ECC83 and just not wire the heater of the spare half, unless the reason is for space saving.

David

[jay_oldstuff]

It's not a question space its a question of symmetry I'm building a bespoke stereo amp for a friend of mine and they are very particular about looks (comes from them being a graphic designer)

Jay

[Radio Wrangler]

Then nothing looks more like an ECC83 than another ECC83. Not using one half would be invisible above the chassis if you left the heater on.

David

[G6Tanuki]

What about a 6C4?

http://www.r-type.org/exhib/aaa0038.htm

The same electrode-plan was stuffed side-by-side into a dual bottle as the 12AU7.

[julie_m]

12AU7 is the same as ECC82.

If the issue is not one of space but simply that you have half a valve doing nothing, you could strap the two sections of the ECC83 in parallel. That's a little bit less wasteful than strapping the unused electrodes to chassis, and should give lower noise.

[kalee20]

I'ma bit puzzled how a stereo amplifier ends up with an odd half ECC83... can you not put an ECC83 in the middle and use half for each channel? Or are you worried about crosstalk?

[jay_oldstuff]

Originally Posted by ajs_derby

If the issue is not one of space but simply that you have half a valve doing nothing, you could strap the two sections of the ECC83 in parallel.

Now that is an idea, I may we'll give that a try. My other idea was to use the two spare triodes as a stereo phono preamp.

Jay

[PE9ZZ_JO22KI]

Graphic designers are weird. Form should follow function, not the other way around. As Dave sez above, EBC91 is half an ECC83.

Tjerk, 9ZZ

[G8HQP Dave]

When form follows function, the result is often beautiful. The converse can be quite ugly!

[bikerhifinut]

Originally Posted by jay_oldstuff

Now that is an idea, I may we'll give that a try. My other idea was to use the two spare triodes as a stereo phono preamp.

If you strap them together, then if you use a common cathode and anode resistor, remember to halve the values to keep the operating condition the same. or you could use individual resistors of course, but i feel that you might have issues if there's a feedback network going back to the first Valve.

What circuit are you using?

Andy.

[peter_sol]

Very often a record player will use an EBC81 ignoring the diodes.
For instance the Bush RP30 and SRP30

[G8HQP Dave]

EBC81 is, I think, one of the many versions (e.g. 6Q7, EBC90, EBC21?) of the high impedance mu=70 triode with a pair of diodes.

[jay_oldstuff]

I think after all this I am going to just use two ECC83's and ether parallel the two triodes up or try use ng the two spare triodes for a phone preamp. The amp is being built for use with a turntable and it would eliminate the need for an external preamp.

I am u seing the mullard 7W stereo amp circuit as my basis as I've used variations of it in the past with very good results.

Jay

[julie_m]

I don't think you'll have enough gain for a phono stage with just a triode. The RIAA network will eat a few dB. You certainly could use it as the second stage after an EF86 or similar, though.

[barretter]

The classic RCA "preamplifier for magnetic phonograph pick-up" uses the two triodes in an ECC83/12AX7 for a complete circuit.

[bikerhifinut]

Originally Posted by jay_oldstuff

I think after all this I am going to just use two ECC83's and ether parallel the two triodes up or try using the two spare triodes for a phone preamp. The amp is being built for use with a turntable and it would eliminate the need for an external preamp.

If you use the spares for a phono stage, as pointed out earlier you'll only have one triode per channel available. Hope i understood that right.
Unless you use another 2 ECC83 for a phono preamp and then the spare triodes could be useful for the cathode follower output from the phono stage.
I have a circuit that is known to work which I could send you for a MM preamp.

If your friends are so hung up on symmetry then how about just building the amp as normal, and in the "spare" valve socket for symmetry, just wire the heaters up and stick a knackered ECC type in as long as the heaters light up.
ECC83's are not the cheapest audio valves and seems a bit of a waste to me.

Otherwise i think the idea of paralleled valves has the easiest solution with the potential advantage of lowered noise, although I doubt you'd notice.

regards

Andy.