Teeco 610D conversion

[angelodp]

Yes, just re-reading Rob Robinettes start up. Duh....

Ok so in go the tubes. Yes. works but Volume does not? Treble yes, Bass yes.

I have a dual bright cap arrangement on the Volume pot, I'll try pulling that. I also have a 36k on the NFB instead of the 22k? Change that?

Ange

[angelodp]

Yup, its a beauty, I like it. Tones-stack is all good and the volume now working. I'll get back to the bright cap thingy later, but it does not seem to need much as its pretty blackface highs.
Gonna run through voltages and see where I am at.

Sluckey, much thanks, its a nice amp for sure. I am running the 6SL7, 6SN7, 6V6/6V6, 5Y3.

Phil, I know you suggested this a month or more ago....

Loads of headroom and with the NFB switched it gets beasty.

Cheers Ange

[angelodp]

Here is the layout I ended up with. I did not have a 250pf on hand and went with 450pf, so i'll be swapping that out when I get the right value.

Oh, forgot to ask about the raw pot, do you like that feature on this amp sluckey? Is it worth drilling another hole up front? I guess I'll preview it.

A

[angelodp]

Here is the layout I ended up with. I did not have a 250pf on hand and went with 450pf, so i'll be swapping that out when I get the right value.

Oh, forgot to ask about the raw pot, do you like that feature on this amp sluckey? Is it worth drilling another hole up front? I guess I'll preview it.

A

So I have a small issue at pin 7 of the 6SL7. Thats where the signal comes back to the 2nd grid off of the tone stack. As I tap the wire its quite microphonic. I swapped the tube out to a 6SN7, re-flowed solder joints, re-tensioned sockets. If I bend the socket tab (pin7) the amp goes into a rapid oscillation. Once I find the good spot oscillation goes away. Does this seem like the tube socket needs to be replaced?

[angelodp]

Resolved the issue on pin 1 by soldering to the lowering part of the tab. I have a two NOS 6SL7's in there now and it plays very well. I do have some hum when I engage the NFB -defeat switch. I am looking for any recommends on areas I improve to lower the Hum level. With the NFB engaged the amp is pretty quiet.

[angelodp]

Isolated the output as well as the input and the jack for the NFB foot-switch, this has lowered the hum to a very very low level.

Sluckey, I am enjoying this design, especially the use of the RAW control to achieve a desired tone.

I wonder if this design will sustain a MV?

Ange

[angelodp]

Current state of this amp.

[sluckey]

I wonder if this design will sustain a MV?

Sure. Just replace the two 220K grid resistors with a dual gang 250K-A pot. I'd probably use a couple 2.2M safety resistors on the pots.

[angelodp]

So PPIMV larMar minus the bias connection, since this is a cathode biased setup?

[TUBEDUDE]

You can take the bias connection point of the MV and connect it to the power amp cathode to further reduce hum. It reduces heater to cathode transfer of hum. There's a thread here somewhere that has a diagram if needed.

[angelodp]

Hi, I have these readings from this amp. The PD is pretty low? Still have a hum issue with the NFB defeat engaged. Would running this amp with such low PD be an issue?

[angelodp]

Pic of amp

[martin manning]

Cathode biased amps usually run ~90% max dissipation for best sound, so I would consider reducing the value of the cathode resistor. At 200R, it is probably ~2x too big to reach that level. On the hum with NFB disabled, is there a good ground reference for the OT secondary when the NFB is removed?

[angelodp]

Thanks Martin, I'll try that swap on the 200r to 100r 5w. On the ground reference for the NFB defeat, can you explain how I could implement that given the layout shown.

Ok so the layout does not show that I ran the ground reference over to the IEC socket ground. Could that be an issue? Maybe try a different spot for that ground reference than the IEC?

I will adjust the doc to show where I am at currently.

Best A

[martin manning]

I'll try that swap on the 200r to 100r 5w. On the ground reference for the NFB defeat, can you explain how I could implement that given the layout shown.

100R or 120R would be a good bet. If you have another 200 or a 220, tack that across the existing one and see what you get. On the ground, just make sure that your OT secondary is grounded to the chassis. I can't tell if it is or not.