DIY Tube Amp Help...
- Thread starter Jeroth
- Start date
There was an oversight in the original Williamson circuit. They run this stage too hard putting the tube into a region of operation where linearity and thus distortion is compromised. By increasing the cathode resistor to about 1.8K (or as high as 2.7K) this can help increase fidelity (and driver stage output voltage swing). I recently did this mod to my two Eico HF-20 monoblocs as part of my upgrade. They use the same circuit driver stage.
Regarding your filament question. It is common to draw tube envelopes with only the filaments shown in a compact area of the schematic. As you surmised to avoid having to draw long lines all over the page.
I suggest building this as two separate monoblocs. That is a powerful amplifier project and to do it best on one chassis with a shared power supply will take a bit of engineering. Not the best for a newcomer IMO.
Billfort
Addicted Member
Hi Jeroth. Thought I’d throw in my 2 cents worth and I don’t even think it’s worth 2 cents 
.
I just finished a scratch built pair of monoblock tube amps and maybe had the same level of experience as you – built some speakers, crossovers and a solid scrape active crossover from a kit. My amps are based on an extremely simple single ended triode circuit yielding low power (6w) and use a bare minimum of parts. I had a few online resources to help with parts selection and chassis layout, a detailed magazine article (Sound Practices) describing the amp, the considerable help of some great individuals here at AK and to top this off, I did these along with 6 other people who built the exact same amps – 2 of these guys where experienced builders with nice test equipment like an oscilloscope. I’m also pretty competent at CAD and have access to a commercial sheet metal manufacturing plant with NC turret presses.
The reason I point all this out is that even with all this going for me, I STILL had problems, and underestimated how tough it is to scratch build something like this – and what I built appears pretty simple compared to the high power project you are considering.
Just my opinion, but I’d take Rob’s advice and start with a solid vintage piece, restore and modify to taste. At the very least, you end up with a bunch of usable parts, most importantly, the iron and chassis. If you don’t like that, check out the multitude of top quality kits out there – you stand a very good chance of ending up with a well sorted amp that works – all with step by step instructions. Kits give you everything in one box and although some may love the treasure hunt aspect of rounding up all the parts themselves, you wouldn’t believe the hours some of our group spent finding that 1 particular oil cap or high wattage resistor. This gets particularly ugly when you are outside the US (Canada for me) and the price keeps rolling up and up and up. Another nice aspect of vintage or kits is that there are some great support networks out there – don’t underestimate this – you WILL need help and with kits in particular, there are LOTS of people out there who have “been there, done that”. You might not want to overlook the fact that a vintage piece or kit built amp will actually be worth something to someone else someday if you want to move up – scratch built? Well…
I know you already have speakers but this whole DIY thing can be much easier with decent high-efficiency speakers. Building a good 3w tube amp is a whole different proposition than building a good 30w amp. I am amazed how good a 2A3 amp kit like the Bottlehead Paramours can sound - a nice simple, complete, low cost kit with step by step instructions, a fantastic support network and even decent resale value.
Sorry for the rant, but as a total DIY newbie who just struggled through a scratch built amp, I thought my experience might be worth something. Of coarse this is all just my opinion, YMMV, and all that.
Billfort
.I just finished a scratch built pair of monoblock tube amps and maybe had the same level of experience as you – built some speakers, crossovers and a solid scrape active crossover from a kit. My amps are based on an extremely simple single ended triode circuit yielding low power (6w) and use a bare minimum of parts. I had a few online resources to help with parts selection and chassis layout, a detailed magazine article (Sound Practices) describing the amp, the considerable help of some great individuals here at AK and to top this off, I did these along with 6 other people who built the exact same amps – 2 of these guys where experienced builders with nice test equipment like an oscilloscope. I’m also pretty competent at CAD and have access to a commercial sheet metal manufacturing plant with NC turret presses.
The reason I point all this out is that even with all this going for me, I STILL had problems, and underestimated how tough it is to scratch build something like this – and what I built appears pretty simple compared to the high power project you are considering.
Just my opinion, but I’d take Rob’s advice and start with a solid vintage piece, restore and modify to taste. At the very least, you end up with a bunch of usable parts, most importantly, the iron and chassis. If you don’t like that, check out the multitude of top quality kits out there – you stand a very good chance of ending up with a well sorted amp that works – all with step by step instructions. Kits give you everything in one box and although some may love the treasure hunt aspect of rounding up all the parts themselves, you wouldn’t believe the hours some of our group spent finding that 1 particular oil cap or high wattage resistor. This gets particularly ugly when you are outside the US (Canada for me) and the price keeps rolling up and up and up. Another nice aspect of vintage or kits is that there are some great support networks out there – don’t underestimate this – you WILL need help and with kits in particular, there are LOTS of people out there who have “been there, done that”. You might not want to overlook the fact that a vintage piece or kit built amp will actually be worth something to someone else someday if you want to move up – scratch built? Well…
I know you already have speakers but this whole DIY thing can be much easier with decent high-efficiency speakers. Building a good 3w tube amp is a whole different proposition than building a good 30w amp. I am amazed how good a 2A3 amp kit like the Bottlehead Paramours can sound - a nice simple, complete, low cost kit with step by step instructions, a fantastic support network and even decent resale value.
Sorry for the rant, but as a total DIY newbie who just struggled through a scratch built amp, I thought my experience might be worth something. Of coarse this is all just my opinion, YMMV, and all that.
Billfort
Thanks everyone, the reply's have been of a great help! I am still leaning towards this design, mainly because of the power it puts out, and because it looks simple. I also have a contact (Dads Friend) who knows A LOT about electronics (his job is designing and assembling circuit boards etc, and for BIG companies too), so if i get stuck, hell be there to help, he also has some contacts in the Electronic Parts Industry, so he can also help with parts finding. One of my other questions is regarding high-efficiency speakers, what is considered a high-efficiency speaker.
Thanks,
Jeroth
Thanks,
Jeroth