Tube equivalents and eBay claims

[MeToo2]

Has anyone else noticed the rather stretched claims about equivalent tubes made on eBay auctions and other tube sites [and I'm putting this politely]

One tube trader on eBay was selling Russian 6n6p (not a bad tube by any means) as being directly equivalent to a 12av7.

He literally wrote: "These tubes simply replace the 6N6P E180CC ECC182 7062 6829 5965 12AV7"

Now I find this sort of claim not only misleading, but potentially downright dangerous.
Have you seen how different the triode bias curves and power limits are of a 6n6p and a 12av7?

Buyer beware.

Maybe we could make a list of the more outrageous claims here [after all the Prodigy-Pro site hits high on Google searches]?

Or at least point out a reasonably reliable source of equivalents?

e.g. http://home.planet.nl/~rotte322/Gegevens/equivalentset.htm
http://www.tubedata.org/usa2for.html

 

[shabtek]

Ebay is not a reliable source for parts data?

edit: nice fictional description kingston--"forces you to keep listening to music."

 

[Kingston]

I've noticed them too, but I have actually got some great suggestions from there. Buyer beware indeed, but checking datasheets is easy enough, and so is tuning the design to suit the different tube.

Those "direct replacement" suggestions are for guitar and phono preamp audiophool folk who enjoy testing different tube flavours. They don't talk in terms of "too high impedance to drive the output transformer, -3dB point seems to be at 70hz".

Instead they say "creamy bright tone with great responsiveness, doesn't muddy up the low end any more". Or "These seem to have finer sonic pixels compared to [insert random other equivalent], but each pixel is not as lit-up, if you can picture that. Yet there's no denying they have tons of resolution and purity, so the combination of supple richness and resolution forces you to keep listening to music."

(Actual extracts from websites geared for such folk)

But hey, if it works for them, who's to say it's not right.

[edit]

It's mostly the soviet union military tube surplus stores that are making the most outrageous equivalency claims. Here's the best source I've found. This and the original datasheets (which might be cyrillic only)are a very reliable combination: http://www.klausmobile.narod.ru/testerfiles/index.htm

 

[MeToo2]

I got a reaction from the seller to my query about plate curves:

"Yes Sir  You can use it instead of the 12AV7. The only difference is the filament, but the 6N6P goes on 6,3V!!Therefore not direct replace
The curves  are not interesting the sound is another."

Hmm I think I recognize someone of the level of technical knowledge that Kingston so ably described.  :

Just to be clear for any newbies reading this. Firstly, the 12AV7 only requires 0.45A of heater current. The 6n6p requires 0.75A±75mA so you could blow up your heater supply. Secondly the pin outs for the heaters are very different (pin 9 is shield on the 6n6p, so heaters are connected to 4 & 5. A 12AV7 with 6.3V heaters would be connected 4+5 & 9). If you did manage to drop it into a circuit designed for a 12av7 with rewired heaters it doesn't stop there. If the 12AV7 was running pretty hot e.g. 200V anode with 12.5mA bias = Vg of -3V and Rcathode of 240 ohms = 2.5W plate dissipation but within the spec of 2.7W max. A 6n6p in that circuit would be running with 200V anode & Rcathode of 240 ohms -> bias current of ±30mA & Vg of -6-7V (off the curves) with a power dissipation of ±6W, which exceeds the max spec of 4.8W per anode. Assuming of course that your HT power supply can deliver 30mA per anode rather than 12.5mA. The list goes on and on why this is NOT anything like an equivalent tube.

If it wasn't potentially dangerous, I'd find it funny.

 

[kato]

Sometimes "direct replacement" is ebay speak for "not pin compatible."

 

[Kingston]

I haven't actually bumped into quite as dangerous claims as you are describing MeToo2. But then just about every single 6n6p is marked as 6n6p/ECC99.

Which it would be if their heater arrangements weren't completely different! Same story for 6N2P as 12AX7.

I was only taken by surprise by this kind of swapping once. 6n1p is often claimed as ECC88 equivalent, which it would be if it had as low rp or if the heater wasn't nearly double the current (at least pins are equal this time!). My heater transformer handled it fine, but I got plenty of bass drop trying to drive a 2:1 transformer in SRPP configuration. As a first lesson this was a lucky accident. Didn't break anything and started reading datasheets details.

6n1p is a really good sounding tube, by the way, if you can afford the rather outrageous heater requirements for what it does. I have a lot of those and I'm trying to figure out some wasteful application for them. They would be really good tubes as first stages of a guitar or mic preamp but I have plenty of those already.

Now 6N8S and 6N9S and 6N23P, they actually are perfect clones.