Post by bwd on Feb 6, 2022 16:55:10 GMT 12
Hi All,
Long time lurker, first time poster here.
Over the last week, I have been working on building a 10WPC 6L6/EL34/KT88 Single ended amp. For the most part, built out of scrap parts I've had lying around.
This amp has an odd story, it started life as a overly complex built 2A3SET amp.... But how I ended up buying it was one of the most interesting experiences (and luckiest) I've had buying poorly described audio gear.
It all started when a music chap I knew, had made a post wanting to buy an amplifier - as his wasn't working. I asked him what amp it was, and why he thought it was stuffed. Ended out that it was missing "preamp output to amp input" RCA links - told him to connect a cable between them, and well it then worked. He mentioned that his mate had offered him a "valve amplifier", and that if I was interested, he could put me in contact with him. Now, at this point I had no idea what it was, I was expecting some modern Chinese hybrid thing - at least something cheap (in terms of quality).
It ended up being left in a student flat, when the previous owner left the country. The 'owner' told me that it was built by the guy's father somewhere in the EU. What was most bewildering is that it was wired for 115V, with a sticker on the back. It had a crudely cut metal front, power transformer had taken some impact - in result of this it was severally bent. One of the RCA's was hanging loose out of the chassis. A pair of Chinese made 2A3's and GE 6BZ7's where all that I could see. But I thought for $100, it would be a bargain just for the transformers and tubes. When I got a picture of the power transformer (Hammond 302AX) model, I was rather pleased to find it had multiple primary taps.
Had a look at the photos the seller sent me a while back, here was the amp before I started to rebuild it:
This was two or so years ago. Having recently started experimenting with valve Hi-Fi amps again, I thought I'd rebuild it into something with a tad more power.
It was only last week I found out what make the output transformers where - thanks Google Images!
Ended up being budget Japanese made 'Tomiko' ultra linear 5K single ended output transformers.
Retailing on eBay in 2011-2013 for $150USD each. With folks on diyaudio having good experience with them.
Despite it not being designed for audio, I'm using a ECC88 in the front section. Mainly due to having more gain than a 12AX7/ECC83, and it's fairly linear.
Here's the same amp (case, transformers) currently:
Schematic:
Main schematic is inspired by the work of Mikael Adbellah, who started the whole KT88 single ended trend in around 2003.
Grid stopper resistors added and improved power supply. Mind Micro-cap's idiotic rectifier symbols. Yes there is 5V going to it, no it is not connected in the schematic. Smile and nod, please for your own sanity.
Keen to get feedback on it, so if anyone has any suggestions, please let me know.
Cheers!
-Bruno
Long time lurker, first time poster here.
Over the last week, I have been working on building a 10WPC 6L6/EL34/KT88 Single ended amp. For the most part, built out of scrap parts I've had lying around.
This amp has an odd story, it started life as a overly complex built 2A3SET amp.... But how I ended up buying it was one of the most interesting experiences (and luckiest) I've had buying poorly described audio gear.
It all started when a music chap I knew, had made a post wanting to buy an amplifier - as his wasn't working. I asked him what amp it was, and why he thought it was stuffed. Ended out that it was missing "preamp output to amp input" RCA links - told him to connect a cable between them, and well it then worked. He mentioned that his mate had offered him a "valve amplifier", and that if I was interested, he could put me in contact with him. Now, at this point I had no idea what it was, I was expecting some modern Chinese hybrid thing - at least something cheap (in terms of quality).
It ended up being left in a student flat, when the previous owner left the country. The 'owner' told me that it was built by the guy's father somewhere in the EU. What was most bewildering is that it was wired for 115V, with a sticker on the back. It had a crudely cut metal front, power transformer had taken some impact - in result of this it was severally bent. One of the RCA's was hanging loose out of the chassis. A pair of Chinese made 2A3's and GE 6BZ7's where all that I could see. But I thought for $100, it would be a bargain just for the transformers and tubes. When I got a picture of the power transformer (Hammond 302AX) model, I was rather pleased to find it had multiple primary taps.
Had a look at the photos the seller sent me a while back, here was the amp before I started to rebuild it:
This was two or so years ago. Having recently started experimenting with valve Hi-Fi amps again, I thought I'd rebuild it into something with a tad more power.
It was only last week I found out what make the output transformers where - thanks Google Images!
Ended up being budget Japanese made 'Tomiko' ultra linear 5K single ended output transformers.
Retailing on eBay in 2011-2013 for $150USD each. With folks on diyaudio having good experience with them.
Despite it not being designed for audio, I'm using a ECC88 in the front section. Mainly due to having more gain than a 12AX7/ECC83, and it's fairly linear.
Here's the same amp (case, transformers) currently:
Schematic:
Main schematic is inspired by the work of Mikael Adbellah, who started the whole KT88 single ended trend in around 2003.
Grid stopper resistors added and improved power supply. Mind Micro-cap's idiotic rectifier symbols. Yes there is 5V going to it, no it is not connected in the schematic. Smile and nod, please for your own sanity.
Keen to get feedback on it, so if anyone has any suggestions, please let me know.
Cheers!
-Bruno
Electronics Technician - Pitch & Pixel
