balanced across it then, yeah thats usually the better way of doing it.
Heathkit Preamplifier Model WA-P2 Power Supply – What are you using?
- Thread starter tcdriver
- Start date
poorbastards
Active Member
The preamp that has a working pot is playing beautifully. I disconnected ground as mentioned. On the other preamp with the burnt up hum pot, do I just need to connect a resistor across each lead to simulate a hum pot. I measured the working pot at around 2.2ohm
No way is any humpot only 2.2Ω. Most are 50Ω to 200Ω. You're seeing the resistance of the parallel filaments. There are various ways to do what you need. Here's a good link that describes the artificial centertap and elevated heaters.
Valve Wizard - Heaters
Jack
Valve Wizard - Heaters
Jack
poorbastards
Active Member
I'll have to dig through that again. When you disconnect the ground you still have continuity from one end of the pot to the other, so I figured a resistor of some sort is needed
No, you do not need to connect any resistor(s) to replace the bad hum pot. The hum pots can be completely disconnected, or left in place, once you remove the ground connection. If you completely disconnect the hum pots it will reduce the load on the 6.3V DC supply by 0.25A, which is good.
poorbastards
Active Member
Okay thank you, I'll need to figure out what's going on then. One preamp with the hum pot left in and ground disconnected, it works great.
The other preamp with the hum pot completely bypassed has an awful hum.
Looks like I need to look it over side by side with my working preamp
Thanks
poorbastards
Active Member
I got it all sorted out, something completely out of left field. I should have tried checked all of the work, there was a grounding issue elsewhere. Can't trust the work of somebody else!
Both sound great except for the crackle in the right speaker. I'm fairly certain it's a bad tube, had the same issue in a monoblock amps I finished up a few months ago. I think I threw the tube back into the stash!
Thanks for all the help, I'm still learning so I appreciate the patience as well. Have a great memorial day weekend!
Both sound great except for the crackle in the right speaker. I'm fairly certain it's a bad tube, had the same issue in a monoblock amps I finished up a few months ago. I think I threw the tube back into the stash!
Thanks for all the help, I'm still learning so I appreciate the patience as well. Have a great memorial day weekend!
poorbastards
Active Member
It's been about a month and I'm loving this setup. However, I tried phono the other night and I just don't get why I'm not getting anything from left or right. I tried to ground the TT to the power supply first and I didn't have anything. All settings on RIIA.
TT ground on either preamp gave me a ground hum on the opposite preamp.
Not sure what I'm doing wrong here. I'll move this to general help if need be. Thanks
TT ground on either preamp gave me a ground hum on the opposite preamp.
Not sure what I'm doing wrong here. I'll move this to general help if need be. Thanks
Have you checked the level setting controls on the back of the unit? Have you tried the Microphone inputs for sound?
So I'm just finishing up building WAP2PS02 for 2 preamps. I used 1N4007 for my bridge rectifier instead. With no load attached B+ is within spec, but as soon as I plug one of the preamps into the power supply I barely get 70v when measuring at the filter cap of the preamp.
Is this an issue with the diodes I chose not being able to handle the load?
Is this an issue with the diodes I chose not being able to handle the load?
Thanks. Both preamps have the 300v can caps so they both need to go no matter what. Will report back once those get replaced.
Ok, back to it! Got both amps working using Power Supply #2. Now I'm going to ask what may be a pretty dumb question.
When I have the preamps hooked up to the PS individually I get good voltages at all my test points (both amps show good voltages). As soon as both are hooked up voltages drop (ex. Pin 1 on V1 is 196v and then drops to 172v). According to the Heathkit manual these amps only need 300v at 10ma, transformer 261G6 says it can do 130ma. Is my voltage drop a function of over taxing the PT? Is there something else I'm missing here?
When I have the preamps hooked up to the PS individually I get good voltages at all my test points (both amps show good voltages). As soon as both are hooked up voltages drop (ex. Pin 1 on V1 is 196v and then drops to 172v). According to the Heathkit manual these amps only need 300v at 10ma, transformer 261G6 says it can do 130ma. Is my voltage drop a function of over taxing the PT? Is there something else I'm missing here?
Are you still using that small PCB with the LM2596 buck converter? I have a bag of those that I bought a few years back, and every one of them is counterfeit. The ICs oscillate at a much lower frequency than a real LM2596, and they can't handle the current of the genuine part. I think they are a different part number that has been shaved and re-stamped. You might want to check the current draw and voltage at the 6.3V supply when both preamps are connected. If the buck converter isn't working correctly, it might be loading down the transformer. The best part to use for this is the XL4016. This is an IC that was actually designed and manufactured in China. They have worked really well for me.
You can find more information if you search the Tube Audio forum here for XL4016 posts by me. And here is a post with links to more info on the counterfeit parts.
Jack
You can find more information if you search the Tube Audio forum here for XL4016 posts by me. And here is a post with links to more info on the counterfeit parts.
Jack
No, I'm actually using the PS drawn out in the quote.
But I will check the current at the heaters later tonight.