Valves, I think I'm starting to understand what the fuss is about.

[HighFidelityGuy]

Dave, I've found the Takman resistors very good. Cheap too.

Thanks Ali. I've used them before and found them to be good. I'm actually using a couple in this project as I couldn't get Kiwame's in a certain value. I'm also using some tantalum resistors in another place for the same reason.

I'd go for the Solens out of the two, they are a little more specialised where as the Evox-Rifa are more general purpose as far as i'm aware

I'm sure there are a bucket full more out there though so take your time. Whilst it won't have any audio signal passing directly through it it still one of the most important caps in the amp keeping the voltage on the front end stable.

Thanks Mark. I've ordered some 0.6uF Solen caps as they were the biggest that would fit on the back of the PCB. I think they'll be easier to fit than the Evox ones as well.

I've now got all of the components mounted other than the few power supply related caps that I'm ordering now and the parts relating to the heater supply. The heater supply is proving tricky as there's not much room to mount the extra components required for the Schottky diode upgrade. So I'm just trying to puzzle that out. I'll post some photo's ASAP but I seem to have mis-placed my camera at the moment.

[HighFidelityGuy]

I found my camera last night, so here's a photo of what I've done so far:



I've now installed the DC heater supply parts and wired up the AC heater supply. As you can see the PCB is getting rather busy. All the components I've used are physically larger than those they replaced which has presented some challenges. The DC heater supply was particularly tricky which this photo attempts to show:



I've used 4700uF Rubycon YXF high ripple, long life caps for the DC heater. I wrapped these in heat shrink to prevent shorts caused my the tight packaging. I just hope I've wired this bit up correctly. I've tried to make it so it's not too tricky to swap the resistor just in case I need to tweak the value to get 6.3V.

Here you can see how the brown Elna Silmic II electrolytic and black Mundorf axial cap's on the right are much bigger than the spaces on the PCB which forced me to do some stacking and packing. You can also see how I've directly soldered a grid resistor to the valve base to get it as close as possible. I've done the same thing with all the grid resistors.:



I've now ordered the last few caps I need. I'll be using a 220uF Panasonic high ripple cap in position C1 and 100uF Vishay low ESR caps in position C2 and C3. So while I'm waiting for them to arrive I've started some work on the case and cabling related stuff. I've removed the input selector, volume control, input sockets and speaker binding posts. I'm going to fit a pair of WBT Nextgen copper RCA sockets for the input and some Eichmann Tellurium Copper speaker binding posts. I'm also upgrading the Zobel network components to Mills wirewound resistors and Mundorf Supreme caps which will be soldered directly to the back of the binding posts. All the internal wiring will be replaced too. Probably with 5N silver wire in Teflon sheathing but I've not quite decided yet. That's all for now.

[colinB]

Have you tried Ampohm oil paper caps? They appear to be going for good prices at the moment and have a big selection including copper.

[HighFidelityGuy]

Have you tried Ampohm oil paper caps? They appear to be going for good prices at the moment and have a big selection including copper.

I did consider them early on but I guess they didn't score as highly as the Mundorf Silver/Oil's in the reviews I read so I discounted them. There are so many makes and models out there I'll probably never try them all. I'm fairly new to DIY Hi-Fi, so as I've not tried many makes I'm quite reliant on recommendations I read online. I guess eventually as I try more I'll settle on on some favorites.

Have you compared the Ampohm's against any other caps?

[colinB]

I havent Dave. There is a mod for my tube amp but it involves Jensen caps and they cost a bomb. Always looking for a cheap oil/paper alternative.

[HighFidelityGuy]

All the parts I was waiting for arrived earlier this week and I managed to finish building the amp back up tonight. After a thorough check over to make sure I'd not made any obvious errors I fired her up to check some voltages. No bangs, no smoke and I didn't get electrocuted, so it's all good so far! Some voltages seem a bit high, some a bit low but hopefully they're within tolerance. I'll have to check that out further but for now it seems to be working. So I'm going to tidy all the crap off my workbench (or "the dining room table" as my wife calls it ) and hook the amp up to some cheap speakers for the first listening test. I'll then break out the oscilloscope and check out some waveforms. I'll try and take some photos too. They're jobs for tomorrow though. Now it's time for a beer, then bed.

[HighFidelityGuy]

Well it makes sound.
I can't really tell what the sound quality is like yet as the £10 Argos speakers I use for testing are offensively crap. I'm going to leave it running through them for at least a couple of hour just to make sure the amp seems stable. I'll then take a few photos and hook the amp up to my main system.

[DSJR]

Yes please to pics.

I do have to say that after listening to the Albarry power amps the other day, I should confirm that solid state CAN do it with careful design and a beefy power supply - not to get oodles of Watts, but to put some inertia behind the Watts that DO come out, if you see what I mean. Hobby-ists that can make their own (valve) gear using good circuits and components for not too much dosh can grin from ear to ear IMO

[HighFidelityGuy]

Yes please to pics.

I do have to say that after listening to the Albarry power amps the other day, I should confirm that solid state CAN do it with careful design and a beefy power supply - not to get oodles of Watts, but to put some inertia behind the Watts that DO come out, if you see what I mean. Hobby-ists that can make their own (valve) gear using good circuits and components for not too much dosh can grin from ear to ear IMO

I know what you mean and I've come to the same conclusion. The power supply seems to play a massive role in determining the end results. My 550W solid state mono-blocks sound great to me but the tiny 15W KEL84 in bottom of the range spec sounded almost as good overall and better in some areas. So I really can't wait to here what it sounds like with all the power supply and signal path mods I've done.

As requested, here are a few photo's of the amp:



The bottom box is my old MD player that's currently looping Jamiroquai. The box at the back is my Lighter Note passive attenuator. The blue LCD is a mains voltage display that I got off eBay recently. It's been calibrated with a Fluke meter that can just be seen in the bottom right.

I couldn't resist doing a valve glow closeup. It'll look better at night but never quite as impressive as the bigger output valves like KT88's. Oh well, they still looks nice and are chucking out a fair amount of heat, as is the mains transformer. This has been mounted of some silicon bushes that I made to raise it up a bit to allow better air flow and dampen the slight hum it makes. The hum has definitely been reduced, so I'm happy about that as this was one of my only real criticisms of the amp. The valve dampers were bought of ebay and seem very good quality even if they do look a bit daft.





Once the amp's been running for another hour or two I'll let it cool down so I can take some photo's of the inside.

EDIT: I forgot to mention that I've left the front panel off for now. I need to sort it out so I can mount the control knobs back on to preserve the aesthetics. The knobs won't actually control anything as the amp's been converted to a single input power amp.

EDIT2: I probably ought to apologise for the blue power LED that I fitted. The original was an orange one that just didn't match my other equipment that all came with blue LED's. I know some people hate them but you can't please everyone.

[HighFidelityGuy]

I've just checked for audible hum and hiss and I can't hear any hum and just a slight bit of hiss when the volume is cranked all the way up. So I'm happy with that.

The only slight cause for concern so far is that the mains transformer is almost too hot to touch. I've read that they run hot in the KEL84 but I'd prefer to lower the temp if possible. Does anyone know if attaching heatsinks to the transformer sides with heat conductive epoxy will affect the working of the transformer at all? I wouldn't have thought so as aluminium isn't ferrous but I thought I better check to be on the safe side. Cheers.