Question for EAR 834P users (rolling tubes)

Hi All,

I have recently purchased an EAR 834P phono preamp second hand.

For those who have changed tubes from the original stock, what tubes did you use? What sonic differences did you notice? Where did you get your tubes from and how much?

Thanks

 

I found out through experience thst some supposed better tubes are rated differently voltage wise.
They are classed as the same tube.
Glen croft and H. Jan, advised caution
When I bought some ECC83,s.
They were JJ,s I ended buying standard .JJ,s

 

Stick to the stock valves or an EXACT substitute.
The circuit of every valve is designed according to the valve's spec sheets for minimum distortion within the working range.
Don't defeat this by substituting a different valve, results always uncertain or bad.

 

Not always. I'm using an English made from the 50's early 60's Raytheon with short and smooth plates for the buffer tube and the results are great. If you choose THE RIGHT TUBE for the buffer tube you can use a 12AU7 tube as it uses exactely the same voltage as 12AX7 tubes and get good results, but I guess it's just a matter of taste.
I also have two 12AU7 tubes, one Japanese made NEC and one Japanese made Hit Ray (joint venture during the 60's and 70's between Hitachi and Raytheon) and both sound great. I have a couple of RCAs, one 12AX7 and one 12AX7A and 'though sound great as buffer tube I much prefer the other three 12AU7 I have. The buffer tube keeps impedance low,it doesn't do amp, I'd never use another tube on the other two sockets that's not a 12AX7 and it's variants (12AX7A, 7025...).

 

See the datasheets of 12AX7 and 12AU7. Then conclude yourself what you are doing.

 

What Am I doin? To my understanding the differences between 12AX7 and 12AU7 is that the first has more gain than the second, but the buffer stage has no gain.

 

In some designs that can work...poorly. And in other designs, that can actually cause harm to the circuit.

I know that in guitar circles it is common place to substitute wildly different tubes into amps, and not generally release the smoke. Often the amp still functions adequately without being damaged because the circuits are unregulated, and because every stage is usually capacitively-coupled, and because you don't have an RIAA curve which you are trying to conform your frequency response to.

But the same can not always be said in the world of hi-fi. Often times in cathode followers are direct coupled to the previous stage inside of hi-fi designs for performance reasons. And often the power supply circuits are regulated (with regulators which can be very easily fried). And whenever tubes are direct coupled to one another, the biasing and loading of each of the tubes becomes inter-twined in ways that can sometimes actually cause damage to a circuit when one tube accidentally gets biased way too hot because an electrically incompatible tube was inserted into one of the sockets.

So substituting low mu tubes into high mu designs or visa-versa is just a fundamentally bad idea with hi-fi gear.

However, that said, you can still roll tubes like crazy inside of your hi-fi gear just as long as you use electrically equivalent types of tubes from as many different manufacturers as you like. There is nearly zero risk of causing damage if you follow this approach. And surprisingly, the sonic differences between perfectly testing electrically equivalent 12AX7s/ECC83s/7025s from different makers can sometimes be shockingly large.

So definitely go for rolling of different brands of the same type of tubes. But it is not wise to roll something like a 12AU7 into a 12AX7 slot, or visa versa.

 

Thenks for your reply. In this case I'm using a different tube, a 12AU7 instead of a 12AX7 on the V3 which is used as a "buffer stage" to keep inpedance low, not on the V1 which does some amp or the V2 which does RIAA reequalization and also some amp. I think it's a good idea to use a 12AU7 on the buffer stage of this Phono preamp as a buffer stage doesn't do amp, it doesn't add any gain, voltage is the same as 12AX7, it only uses more current but the power supply on the EAR 834 is beefy enough for that, and also a 12AU7 has less gain but it outputs more current and has a lower impedance output, perfect as a buffer tube!!!
In fact Tim de Paravicini, the designer of this Phono preamp was asked on an interview about the use of a 12AU7 on the V3 tube instead of a 12AX7 and he said that he wouldn't do it, that he designed hisPhono preamp with use with 3 12AX7's but that there can be cases when an specific model or brand of 12AU7 may sound good and suit the tastes of the owner/listener better. He was also asked if there was any danger at using a 12AU7 on the V3 instead of a 12AX7 and he said no, that there wasn't any danger at all. So my English made Raytheon 12AU7 from the 1950's stays.

 

There's additional information from our Host on a previous thread....

What are the stock ECC83 tubes in the 834P

 

Use a good 12AU7 on the V3 tube (closest to the front) as this tube is used as a "buffer" tube to keep impedance and distortion as low as possible, and 12AU7 as a low impedance output (lower than a 12AX7) and a high current output, its gain is lower but this V3 tube is not used to do any amping.
I'm using an English made Raytheon with almost black,short and smooth plates 12AU7 on the V3 tube and the difference with the RCA 12AX7A from the 60's I was using before is night and day.
Using a 12AU7 on the V3 position won't harm your Phono preamp in any way,this even has been stated by Mr. de Paravicini himself. He was asked why they designed and shipped the EAR 834P with 12AU7 instead of 12AX7 and he answered that the 12AX7 gives a more accurate (aka: neutral,flat sounding) sound next to a 12AU7 that seems to enlarge the sound stage and color sound in a "tubey", warmand sweet charasteristic sound.
Just in case anybody is interested on these tubes here's the link for them. Tell Dan or James to send you an English one as not all of them are English made.
ECC82 12AU7A RAYTHEON NOS VALVE/TUBE (LC9) | eBay