playloud
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Picked this up for ~$US200 locally:
The back story of these amps is that they were made in Christchurch, NZ by a guy called Ron Holden, and imported to Australia under the name "Wasp", presumably to avoid conflicts with the Aussie car brand. Angus Young supposedly used one in the early days of Acca Dacca and - if this thread on the Metro forum and the opening seconds of the 'High Voltage' video can be believed - it was the Wasp-branded version of this particular model.
The seller said he could only get a "buzzing sound" out of it but, on inspection, it appears this was only when using one input jack! A bit of contact cleaner later, and it was running fine. The chassis had a fair bit of dust on it, but I cleaned that away with a toothbrush
The power tubes are GEC KT88s (better start saving for replacements, as they look quite worn!), and preamp tubes were all relabeled Heerlen ECC81/ECC82. I actually suspect these were replacements, as V1-2 would surely have been ECC83s originally (and this agrees with what I've read over at Oz Valve Amps - although the schematics posted there vary a bit from this one). I replaced those with ECC83s (a long plate Mullard and Telefunken - only the best for those KT88s), and the amp sings!
Here's a clip with the LP straight in:
When I bought it, I was open to the idea of converting the preamp to something Hiwatt-like, given the tube complement and general appearance. Having heard it, however, I think that would be a travesty!
The power supply is similar to the Gunn I worked on previously, in that the plate voltage is incredibly high (692V at idle) and the screens are about half that. I haven't got out the scope, but power output is comparable to a 100W Marshall (if anything, the levels into the DAW when recording are a tad hotter). I've biased it at a conservative 30mA (50% if using the "absolute max" 42W plate dissipation in the GEC datasheets).
The phase inverter is curious, in that it has an ECC82 cathode follower stage (V4) for each of the regular LTP PI outputs (V3). There's also a pot on the chassis forming a voltage divider before the power stage grids, which seems to be a manual method for "finetuning" the PI balance?
The construction is generally quite good. PCBs look well-constructed, and the transformers are certainly formidable (although the paints peels off the end bells whenever you touch them!) It's an odd layout, however, with the pots, preamp and power amp all being in distinct locations.
For now, I plan to only make the following changes:
- Move the in-chassis fuse from the primary neutral (which seems redundant) to the HT (for when a KT88 inevitably blows!)
- Replace the bias filter cap
- Beef up the other filters somewhat, probably starting with 50+50uf cans for the mains voltage doubler (I don't mind some ghosting, but you can tell this amp wants to be aggressive!)
Other than that, it's a great amp as-is! I hate to say it, but it's not that hard to imagine a parallel universe in which Angus never switched over to Marshall
The back story of these amps is that they were made in Christchurch, NZ by a guy called Ron Holden, and imported to Australia under the name "Wasp", presumably to avoid conflicts with the Aussie car brand. Angus Young supposedly used one in the early days of Acca Dacca and - if this thread on the Metro forum and the opening seconds of the 'High Voltage' video can be believed - it was the Wasp-branded version of this particular model.
The seller said he could only get a "buzzing sound" out of it but, on inspection, it appears this was only when using one input jack! A bit of contact cleaner later, and it was running fine. The chassis had a fair bit of dust on it, but I cleaned that away with a toothbrush
The power tubes are GEC KT88s (better start saving for replacements, as they look quite worn!), and preamp tubes were all relabeled Heerlen ECC81/ECC82. I actually suspect these were replacements, as V1-2 would surely have been ECC83s originally (and this agrees with what I've read over at Oz Valve Amps - although the schematics posted there vary a bit from this one). I replaced those with ECC83s (a long plate Mullard and Telefunken - only the best for those KT88s), and the amp sings!
Here's a clip with the LP straight in:
When I bought it, I was open to the idea of converting the preamp to something Hiwatt-like, given the tube complement and general appearance. Having heard it, however, I think that would be a travesty!
The power supply is similar to the Gunn I worked on previously, in that the plate voltage is incredibly high (692V at idle) and the screens are about half that. I haven't got out the scope, but power output is comparable to a 100W Marshall (if anything, the levels into the DAW when recording are a tad hotter). I've biased it at a conservative 30mA (50% if using the "absolute max" 42W plate dissipation in the GEC datasheets).
The phase inverter is curious, in that it has an ECC82 cathode follower stage (V4) for each of the regular LTP PI outputs (V3). There's also a pot on the chassis forming a voltage divider before the power stage grids, which seems to be a manual method for "finetuning" the PI balance?
The construction is generally quite good. PCBs look well-constructed, and the transformers are certainly formidable (although the paints peels off the end bells whenever you touch them!) It's an odd layout, however, with the pots, preamp and power amp all being in distinct locations.
For now, I plan to only make the following changes:
- Move the in-chassis fuse from the primary neutral (which seems redundant) to the HT (for when a KT88 inevitably blows!)
- Replace the bias filter cap
- Beef up the other filters somewhat, probably starting with 50+50uf cans for the mains voltage doubler (I don't mind some ghosting, but you can tell this amp wants to be aggressive!)
Other than that, it's a great amp as-is! I hate to say it, but it's not that hard to imagine a parallel universe in which Angus never switched over to Marshall
