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Hi Everyone, I recently picked up this 6B4G push pull amplifier. I normally just stick to single ended amps but, I thought this would be fun to play with. My thoughts were that the extra power would give me the ability to use less efficient speakers and I love the sound of 2A3/6B4G's. The...

Hi Everyone, I'm fortunate enough to go to a college with a learning lab that encourages independent study. I decided I would like to study speaker design for my project and I'm currently doing research. Having been in the hobby for a while now, I've heard some amazing speakers and I'm...

Hi Everyone, I recently picked up a cheap Lepai 2020TI to mess around with. I connected to my bench equipment since I was curious to see if it would meet spec. I connected it to my Variac set to 120 volts, my HP8903B audio analyzer, and my 8 ohm 1% non inductive dummy load. I've tested a...

Hi Everyone, I was working on a pair of Quad ESL 63's that were beginning to show signs of aging. One speaker had reduced HV, which was causing slightly reduced volume but, other than that they were operating alright. I thought I might as well replaced the parts on both EHT boards if I was...

Hi Everyone, I'm having trouble with a Hafler 220, one channel is dead. If you go to adjust the bias which according to the service manual is suppose to be set to 275 mA, all I get is 3.86 mA and it doesn't change if you adjust the pot. I pulled all the transistors on the driver board but...

Hi Everybody, I'm trying to decide on a preamp for my current setup. I don't mind going with new or vintage but, I would really like a remote, I guess if it was a killer deal on a vintage I could run the wiring to place the pre near the seats but, if I could avoid that I would be happy...

Hi Everyone, So I've got that itch to build something again and I've come across an old argument with B+ filtering that I've heard before and I would like to get everyone's thoughts on the subject. I'm not sure about everyone else but, idle hum bugs me, I think we've all been there...

Hey Everyone, I was doing research for my next build and was excited that I was going to go with all James Audio transformers this time and I've heard that they've gone out of business this past April :( Is this true? If it is, does anyone know of transformers of their quality at...

Hi Everyone, Earlier this year I bought and restored a Citation 16 and the only thing I didn't replace was the outputs. I was getting about 0.03% THD but the power wasn't the rated 150 watts at 1.25 volts (it was about 136 watts). So I thought I'd bite the bullet and replace the outputs...

Hi Everyone, I recently traded for a pair of Quad ESL 63's (US studio version). The problem one is currently having is that it's playing back at reduced volume, no pops, hiss, crackles, or distortion, just reduced volume. After thumbing through the service manual it seems like it's probably...

Hi Everyone, I was changing the belts for my Uncle on his TEAC V-3RX deck and discovered that the idler tire had turned into a gooey mess. I've been trying to find a replacement but I've been coming up dry. From what I found from searches TEAC never sold just the tires you had to buy the...

Hi Everyone, I'm restoring a piece of equipment that used MPSU10/MPSU60's (without heatsink they're rated for 1 watt) which are out of production, I found that a poplar replacement was MPSW42/92 but, they too are phased out. The closest in production transistor that I could find is...

Hello Everyone, I have a Citation 16 with what I believe are bad UA739PC's, the amp only uses half of the UA739PC so I was wondering if I put in a NE5534P and rewired would that work? The voltages are within the spec and the bandwidth match but I'm just not familiar with IC's to know if...

Hi Everyone, I recently purchased a HK Citation 16 to replace my current main amp but, I want to give her the royal treatment before she becomes my main amp (it's kinda ugly and beefy maybe it's a him? haha) I'm going to replace all the electrolytic capacitors, trim pots, output...

Hi Everybody, I recently purchased a Citation 16 which I'm going to rebuild. Now I know the common stuff like replacing all the electrolytic caps, deoxit the controls, re-grease the output transistors if the thermal paste is dried up etc. I was wondering about some of the other mods I've...

Hi Everyone, I have a 510 that I've been working on for a friend that isn't cooperating :-P I replaced all the electrolytic caps except for the two large main filter caps, I adjusted the bias and DC offset, but I'm not getting the 0.05% distortion that the service manual states. I know that...

Hi Everyone, I recently built this circuit: http://www.dmitrynizh.com/moondog-choke-dc-doubler-compl.gif it's supplying 12.4 volts DC but, the filament looks pretty bright compared to the other channel that I left AC for comparison, and R2 the 0.15 ohm resistor got so hot it started to...

Hi Everyone, I'm working on a Marantz 510 for a friend and after some hunting discovered his troubles were from a faulty driver board. One channel is putting out about 100 watts less than it should and when I swapped the driver boards it followed the board, and I had done the bias...

I recently picked up an amp that another wasn't able to build which had almost everything already to go for assembly. So I followed the diagram that they were basing the circuit off of and I'm having low frequency hum trouble (varies from 180Hz - 405Hz my scope also picked up a signal 1.3MHz -...

Hi Everyone, I need help designing a mixed bias circuit for my 6336A amp, it's currently cathode bias but it's 114 mA and 134 mA a section and my power transformer is only rated for 200 mA so I was hoping to bias it to 99 mA a section. The other reason for moving to mixed bias, beyond...

Hi Everybody, I'm helping my friend build a Fairchild 670 clone and the B+ is fluctuating, It's strange since a couple times it ran without that problem but @ 170 volts (it's suppose to be 240) then the power went up to 240 volts but started fluctuating, last time I turned it on it's now...

Hi Everyone, I'm helping a friend wire his Fairchild 670 tube compressor, and came across a symbol on the circuit diagram that neither of us are sure of what it means. I circled it in red. Thoughts?

Hi Everyone, I'm a little puzzled at the moment, I have two C35 Preamps and one has male XLR outputs and the other has female. I don't understand why you'd want a female XLR as an output. I just find it a little annoying since I'm going to have to buy adapters, and I know they're not going to...

I'm struggling with the 6SJ7's in my 300b amp, I'm much more comfortable with triodes. I did some research and found "Resistance Coupled Amplifier Charts for commonly audio voltage amplifying tubes" which has a chart for the 6SJ7 in pentode configuration, I'm not even going to attempt to figure...

After working out the kinks in my 2A3 amp I felt motivated to give another crack at the MP428, I adjusted the voltages on the 300b's to get them dissipating 38 watts instead of 31.5 watts, and I added balance pots for the 300b's. It has improved it's performance but, from about 200 Hz up the...