NminiAD

JezWynd

Been downsizing my gear footprint recently and as part of that had considered installing the amp of my Laney Cub 10 into the cabinet of an Excelsior that I had knocking around. Then I saw that Wang's had a 5w version of their mini amp - perfect to sit on top of the Excelsior.

Arrived yesterday and I'm pleasantly surprised. It's a weighty little thing and appears well built. It uses a strange combo of valves - 1x 12BH7 + 0.5 x 12AX7 as power valve section, 1.5 x 12AX7 as preamp, plus a 6Z4 rectifier valve. There's also a diode rectifier with an option to choose between the two. Controls are Bass/Mid/Treble and Volume with a Warm/Bright switch.

First impression is that it's bright, loud and very touch sensitive. It's easy to dial down the brightness with the Bright/Warm switch and dropping the Treble a touch. Previously I'd been playing guitar mainly through an Ampeg PF-20 head into a 450w 1x15 cabinet which, while it sounded very good, was overkill for my back room. The Excelsior cab with the Wangs Mini 5 is much less obtrusive and actually sounds better for guitar - more top end/sparkle and it loves P90s and pedals.

There's a small amount of hiss from the unit that I'm thinking might disappear with some new valves, so I've ordered some Harma's to replace the 12BH7 and 12AX7s. I'm not sure what to do about the valve rectifier - I haven't had a valve rectified amp for a long time and I'm uncertain how much effect replacing it would have. Plus the Chinese 6Z4 uses some funky arrangement of pins apparently, that requires an adapter to replace it with a 6X4. I'll wait a while and see how the new power and preamp valves work out.

I've read some reports online of these units overheating and burning out the internal transformer but I'm hopeful that as I don't use it at high volume it should be okay. Time will tell...

ecc83

I was going to say, get a spare 12BH7. Not because it will fix the hiss OR that they are unreliable but, (and "hai know nathing") but I can see them getting scarce in not too many years. 

I have always found the TAD 7025 HG a good, low noise double triode and not a silly price.   For a 5W amp I would say a valve rectifier is more for marketing puff than any sonic purpose. I understand the "sag" effect is pretty subtle even on big amps that pull a decent HT current? 
I wonder if the BH7 is fixed or cathode biased (bet the latter) ? It might be as well to get a good tech to check it and make sure the anode currents are in spec for the valve? They are tough buggers but excess current could cook the OPT as it will be necessarily wee. 

Dave.

ICBM

The rectifier valve will make no difference to the sound unless you get one that's a very different spec, and even then probably not much. Rectifiers generally last a long time too, but I would *definitely* get a spare as well as at least one spare 12BH7 - as Dave says, these are not standard types and could become impossible to replace before long. I'm not sure I've even come across a 6Z4 before.

JJ and Sovtek 12AX7WB preamp valves are duller-sounding and may help with the hiss.

JezWynd

ICBM said:

The rectifier valve will make no difference to the sound unless you get one that's a very different spec, and even then probably not much. Rectifiers generally last a long time too, but I would *definitely* get a spare as well as at least one spare 12BH7 - as Dave says, these are not standard types and could become impossible to replace before long. I'm not sure I've even come across a 6Z4 before.

JJ and Sovtek 12AX7WB preamp valves are duller-sounding and may help with the hiss.

Internet reading tells me they are a Chinese valve that is v similar to 6X4 but a couple of pins are swapped around, hence the need for an adapter to make them work.

The hiss is slight; could it even be the P90 causing it? Not sure but I thought I'd try some replacement valves. I went with Harma valves for power and preamp; not a manufacturer I've used before but Watford Valves write up sounded promising for the 12BH7 and I thought it might be a good idea to go with the same make for pre and power as they share a valve.

ecc83 said:

I was going to say, get a spare 12BH7. Not because it will fix the hiss OR that they are unreliable but, (and "hai know nathing") but I can see them getting scarce in not too many years. 

I have always found the TAD 7025 HG a good, low noise double triode and not a silly price.   For a 5W amp I would say a valve rectifier is more for marketing puff than any sonic purpose. I understand the "sag" effect is pretty subtle even on big amps that pull a decent HT current? 
I wonder if the BH7 is fixed or cathode biased (bet the latter) ? It might be as well to get a good tech to check it and make sure the anode currents are in spec for the valve? They are tough buggers but excess current could cook the OPT as it will be necessarily wee. 

Dave.

I'm afraid that double triodes, cathode biasing and anode current are things I know nothing about but I'll take your advice and source a spare 12BH7 or two. I'm also unfamiliar with valve rectifiers; I think they are supposed to induce sag, though I imagine that is only going to happen if the amp is being pushed hard? Not something I'm likely to do and I'm not hearing any difference between valve and diode at the volume I'm using.

ICBM

JezWynd said:

The hiss is slight; could it even be the P90 causing it?

No. Pickups hum and/or buzz, but not hiss.

JezWynd said:

I went with Harma valves for power and preamp; not a manufacturer I've used before but Watford Valves write up sounded promising for the 12BH7 and I thought it might be a good idea to go with the same make for pre and power as they share a valve.

Unfortunately that's a mistaken assumption... Harma are not a manufacturer at all, they're Watford Valves in-house brand with which they label other manufacturer's valves. Whether the 12AX7s and the 12BH7 even come from the same country is not a certainty - they use several different sources.

JezWynd

ICBM said:

Unfortunately that's a mistaken assumption... Harma are not a manufacturer at all, they're Watford Valves in-house brand with which they label other manufacturer's valves. Whether the 12AX7s and the 12BH7 even come from the same country is not a certainty - they use several different sources.

There's only one response to that -

JezWynd

Harma valves arrived and installed. Hiss reduced (although not prominent to start with). Most noticeable difference is the increased harmonic saturation in the mids and a general uptick in musicality - less steely exactitude, more chime and richness, so v pleased (really brings out the P90's qualities).  Noting your comments about the possible difficulty in future sourcing of 12BH7s, I've ordered a Phillips as a spare, a bit pricey but says it's military spec so hopefully long lasting.