Tube amp replacement question

September 4, 2016 10:16 AM

I purchased the Monoprice Hybrid Tube Amp with Bluetooth recently and want to upgrade the tubes. Please help!

Hi all,

I recently purchased this amp and love it.

I've read a lot about people upgrading the tubes and being shocked at how good it really can be. As this is a cheap upgrade, I'd like to try it out.

I need to know which EXACT tubes I can put into this. Apparently they went from 6n1 to 6n2 tubes over the course of production changes. The manual I got specifically says 6n2 and 6P15 as the tubes used, even though the product page still says 6n1.

My plan is to purchase 2 EL-84 mullard and 2 6N2P-EV tubes. Is this correct? if so, can somebody possibly point me to the best place to purchase these? Currently looking at 2 different ebay vendors and the total cost will be about $50-60 for all four.

Additionally, if anybody could recommend speakers for this guy I would appreciate it. I'm currently using Pioneer SP-BS22-LR and they're excellent, but I'm thinking of getting a second amp for the garage and would like advice on speakers for this type of amp.


Thanks!

posted by lattiboy to Technology (5 answers total)

6n1 and 6n2 are swappable. The gain is higher with 6n2, but it shouldn't matter so much because the tubes are JUST for the preamp here, not the power amp. Similar for el-84 and 6p15; they seem nearly identical. I've purchase from tubedepot.com and thetubestore.com in the past with no problems. As for speakers, any fairly-high-sensitivity bookshelf speakers should be great, though maybe you want to look at some indoor/outdoor or weather-resistant ones because they'll be in the garage? I searched 'outdoor bookshelf speakers' on Amazon and found a buncha stuff.
posted by destructive cactus at 10:57 AM on September 4, 2016 [2 favorites]

Better speakers would probably be a way more noticeable upgrade. Anything(even whatever their cheapest speakers are) from a hi fi speaker manufacturer such as:
Focal
B&W
KEF
Paradigm
Gallo
Mirage
Rega

This is just off the top of my head. The cheapest offering from any of these companies will sound way better than what you have now.
posted by MjrMjr at 4:52 PM on September 4, 2016

Are you looking only at current production tubes, or are older US, British, and European tubes (aka NOS and ANOS - new old stock and almost new old stock) options as well?

I have bought a number of NOS tubes from Mike K. at http://www.kcanostubes.com for guitar amps. Great guy, fantastically knowledgeable about tubes.
posted by mosk at 9:33 AM on September 5, 2016

It's been a while since I worked with tubes - valves, in old money - but I used to build and repair a lot of gear with thermionics. My experience was that there was a lot of variation between 'identical' parts from different manufacturers, and even different production runs from the same manufacturer. In some applications, you absolutely had to select the right parts by testing their actual specifications and finding individual items that fell within the requirements, and very often make adjustments to their operating conditions once fitted.

Tubes are rarely precision devices, and most tube circuits - especially consumer audio ones - can tolerate a lot of slop. The practical outcome in a hybrid tube amp like yours is that if a different tube makes different audio - which it really might not - it may be because of the individual part rather than the type number change. Also, unlike solid state, tubes age in use, and again that varies a lot with different factors (I have a 60 year old radio with original tubes that's just fine; another from 1980 that needed a factory fitted 12BY7 changed out five years ago because it had aged badly and lost too much emission. Yes, they made radios with tubes in, in 1980).

So if you can try out different options before you spend too much money, I'd recommend it.
posted by Devonian at 3:44 PM on September 5, 2016

My experience was that there was a lot of variation between 'identical' parts from different manufacturers, and even different production runs from the same manufacturer.

This, oh so very much this!

I'm not a valve amp afficionado (I restore old radios), but the specs in valve datasheets really need to be treated as minimum specs. It's really not at all unusual to find 2 otherwise identical NOS valves of the same make, factory, & date/lot markings where one tests 60% or more "better" than the other, particularly on Gm.

(By the way, there's no such thing as "Almost New Old Stock" ("ANOS") when applied to valves that obviously aren't new but test within datasheet specs. What they really mean is "used".

Similarly, the correct term for "used, but tests close to datasheet specs" is "worn out"…)

And really, if you go swapping the valves like that you really need at least the bias for each stage to be adjusted, if not considerably re-designed. The grid cutoffs, currents, and load lines are vastly different between 6N1 and 6N2 (although the 6N2P is close to the latter), and much the same goes for the 6P16 vs EL84 - you can more or less consider the 6P16 as a lower voltage, lower power version of the EL84. To beat the 6P16 at its own game, you'll probably have to up the anode voltage by 50V or so too. (Though, thinking about it, an EL84 might perform minimaly better than the 6P16 at the latter's lower Va? Not going to look that far…)

Devonian, I'm curious what radio (other than maybe a top-end audiophile receiver?) was still using valves in 1980? It's one of those questions that pops up occasionally on antique radio forums, and I think they always end up deciding either on the Aus Kriesler 11-99 (~1974) or some GE-rebadged Japanese set up to ~1976.
posted by Pinback at 10:41 PM on September 5, 2016