50w Hot Rod Plexi AFD #39

[sluckey]

Does anyone have a better source for .68 Caps? The smallest ones that I found were big. I think I bought them from Antique Electronics.

Hoffman has a small one...

.68uf/250v 684
250 volt Panasonic Polyester film capacitor - cathode bypass cap
16.8mm wide x 5.39mm tall x 5.3mm thick
Price each = $1.00

I have some small M150s that I've used in 3 different amps. I don't know where I found them but they were out there back when M150s were yellow. Look on the right end of the board on this Plexi-6V6...

http://sluckeyamps.com/6v6plexi/P-6V6_05_big.jpg

[purpletele]

Does anyone have a better source for .68 Caps? The smallest ones that I found were big. I think I bought them from Antique Electronics.

Hoffman has a small one...

.68uf/250v 684
250 volt Panasonic Polyester film capacitor - cathode bypass cap
16.8mm wide x 5.39mm tall x 5.3mm thick
Price each = $1.00

I have some small M150s that I've used in 3 different amps. I don't know where I found them but they were out there back when M150s were yellow. Look on the right end of the board on this Plexi-6V6...

http://sluckeyamps.com/6v6plexi/P-6V6_05_big.jpg

Thank you Steve!

[M Fowler]

I have a bag of 250 blue metalized polyester film caps .68uf/250v and I also buy smaller yellow .68uf/100v caps that look like those large Sozo caps.


Can't remember where I got those smaller yellow .68uf caps from.


Left me know if you need some of those blue film caps.


Mark

[purpletele]

I have a bag of 250 blue metalized polyester film caps .68uf/250v and I also buy smaller yellow .68uf/100v caps that look like those large Sozo caps.


Can't remember where I got those smaller yellow .68uf caps from.


Left me know if you need some of those blue film caps.


Mark

Question: Why would I be OK with a 100 V coupling cap, unless I know for sure that I will not have more than 100 V that needs to get through the circuit at that point?

I bought the Yellow Zepplin .68 uF 630 V because I thought I needed the voltage range.


Any insight would be enlightening

[sluckey]

You would be OK even with a 15V cap. There's only a couple volts on that cathode cap.

[purpletele]

You would be OK even with a 15V cap. There's only a couple volts on that cathode cap.

Thanks Steve! Stay tuned for the Dual 50 project

[purpletele]

Start Up Notes and Question

I am up and running without an event, if you know what I mean.

The amp is playing ok but it is thin and the MV is not working.

Question 1: On Marks layout he is showing the FX loop Send and Receive jack tied together with a positive leg and also the ground. I am using Switchcraft speaker jacks, and I sure I should be using a switching jack to keep the circuit closed until it is broken by a signal, also I didn't tie the Positive tips together. I suspect that is why I do not have any MV control.

Can I get some guidance on the switchcraft jack and the configuration of the tips.

I have attached a voltage chart. The voltages seem real solid with exception to V4-6. The voltage on that node is jumping all around, so that seems like an issue.


Any feedback on the FX loop jack and V4-6 Voltage would be much appreciated.

[purpletele]

Update

I switched out the FX Jacks to 12A's. I tied the shunt to the tip and then connected the tips together to complete the circuit.

Wowza!! Hello Kitty. It's getting really good now.


I also found a bad ground connection on the MV pot going to the buss, got that connected and the MV works great.


Really pleased so far. I'll test the FX loop to see if I double shunted myself.


I don't understand V4-6 voltage jumping around? But the amp seems to be playing really well.


BV

[sluckey]

Which schematic are you working from? Is V4 a LTP PI? If so, does pin 6 settle down if you disconnect the NFB loop?

[M Fowler]

Yes for Switchcraft type jack it's wired together (12A) type. See 2nd attachment below.

Here is the preamp schematic, power amp schematic is normal 2204 or 2203 Marshall.

Mark

Darkbluemurder high gain amp.gif

DBM #39 layout W loop.jpg

[purpletele]

Yes for Switchcraft type jack it's wired together (12A) type. See 2nd attachment below.

Here is the preamp schematic, power amp schematic is normal 2204 or 2203 Marshall.

Mark

Darkbluemurder high gain amp.gif

DBM #39 layout W loop.jpg

Thanks for the Switchcraft layout advice. I ended up doing that exact configuration late last night.

My issues at this time is the floating voltage at V4-6, which I will play with shortly, I have a decaying note issue when the boost is engaged, and the FX Loop is giving me Deep Six Submarine Pings.

The amp is extremely quiet and stable, the bias is set at 40.5 mV and it just rips.

BV

[purpletele]

Which schematic are you working from? Is V4 a LTP PI? If so, does pin 6 settle down if you disconnect the NFB loop?

I disconnected the NFB and re-measured the voltage at V4-6 and it is still jumping around. It cycles from OL to a low mV value to a low voltage value.

The amp is stable and sounds good. I don't understand the voltage fluctuations and how I can be sounding good with that chaos.

BV

[sluckey]

What kind of meter? Try another meter. Cycling from OL to low mV is not a characteristic of an amp that is stable and sounds good unless you are Neil or Eddie.

[purpletele]

What kind of meter? Try another meter. Cycling from OL to low mV is not a characteristic of an amp that is stable and sounds good unless you are Neil or Eddie.

My meter is a newer Klein, I'll try another meter and make a video. Thank you

[M Fowler]

I would just reflow the solder joints for V6 and see if that helps.