Teeco 610D conversion

[martin manning]

Nice! looks good now (well, much better, anyway). Definite replace the other wax caps

[angelodp]

Martin, on V1, the 6SC7, there is a wax cap .01 in series with a 220k R from Plate to Grid 2. I just tried replacing that with a new .01 715 cap and the amp was motor boating like a tremolo with that new cap. I put the old cap back in and all is well?? Does that make sense? You can see that network on the layout, albeit a spaghetti factory.

Ange

[martin manning]

My guess is you've restored the bias on the second triode and exposed a deteriorated power supply filter cap. If you measure voltage on that grid with the old wax cap installed what do you get?

[angelodp]

Hi, I am seeing 1.57V at the grid, so it is leaky. The can caps are probably the original ones, but maybe they have been replaced some time ago and still not great.

[angelodp]

I added a series 22uf 400v to the power cap node thats feed the plate on V1. That lowered the DC to almost nothing. With a new .01 series cap between the grid and plate, as before the amp still motorboats. With the old was cap back in its clean and does not motorboat, but there is some DC leak on that wax cap. Not sure what to make of this.

Ange

[angelodp]

Just added another new power cap 22uf 450v at the very first B+ node in series. The wax cap lets in 1.68v DC and the amp works fine. The new coupling cap (swapping the wax cap) now in still causes oscillation akin to a tremolo effect. Not sure what to try next.

[martin manning]

Series? Paralleling a new cap in is what you want to try. However, fixing up the first node is not going to help with decoupling the later stages. For a test you could try paralleling new caps in on the preamp nodes (the two-section can on the left in your drawing), but I'm thinking you will probably need to recap the whole thing.

[angelodp]

Yes, sorry I did parallel not series, misspoke. I tried at the preamp section and at the first node, but still had the issue. I reckon this is just too messy, I'll get back to re-working with a new board, caps etc, more of a 5C3 idea.

thanks A

[angelodp]

Ok I do have a solution to the oscillation. It occurred to me that coupling cap that I was replacing, .01 had a tremolo effect that changed with a lower value cap but still oscillated. Just on a stab I put in a 47pf 500v cap in and bingo no oscillation, albeit a bit thin and unpleasant. I up'd the cap to 500pf 500v and its all working with no oscillation. I am gonna borrow a scope to see whats what, hopefully the oscillation has not gone in-audible and wreaking havoc. Thats where I am at thus far. Kinda stinging cleans that goes into breakup at 8-9.

[angelodp]

Hi, I am kindly asking for help on this tone stack before I make the full on conversion to 5C3. I have taken this weird tone stack out ( which kinda works, but has no bass control) and put in a standard Fender TS, which produced buzzing and weird tone and was a mess. This tones stack is the remnant fo the HI-Fi original stack.

Volme works fine,

Treble is only marginal

Bass almost nothing and cuts out when fully dialed in.

Is there a simple rejiggering that would allow some bass control and better treble?

Hope I can get any suggestions.

A

[TUBEDUDE]

Have you replaced all filter caps yet?

[angelodp]

Yes caps are replaced. I might just rip apart and do the Fender circuit, but just curious about this very strange tone-stack and if there is a quick fix.

[TUBEDUDE]

You've already ripped it out and replaced it with the Fender stack, right?

[angelodp]

yes and that was a mess. So old stack is back and works marginally??

Volume fine with ok tone

Treble, not much change

Bass very little change and cuts out when dimed

[TUBEDUDE]

Check that .001uF in the tone stack.