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I think it will help some for sure.
I hate the JJ12at7..........yes hate is a strong word, but they suck!

In my opinion a good Mullard or brimar/amperex in the the PI is the second most important tube in a HIWATT.

I do not like 6550's in HIWATTs at all, I have put JJ KT88's in both my DR201 and DR405's they are great tubes and four of them will work fine in your amp.

between the JJ12at7 and those nasty sovteks, Yuck! I know how it sounds right now, and it isn't good.

Thank you for the advice. I'll see what kind of change I get from the Mullard PI tube and report back!

you are welcome!

I got that Mullard on Monday and it has seemed to help smooth stuff out a bit! When I have some $ kicking around I'm gonna get a NOS Mullard for the V1 slot. I had the amp open to take pictures for another thread and I noticed a few caps in the pre-amp seem to been replaced at some point. Are these correct or a mod? Sorry for all of the questions, I'm just trying to rule out the possibility of a modification! I'm also a newbie when it comes to amp internals.

the first .047 should not be there. its a mod.
the JJ electrolytics are known for being brittle sounding too.

Dr.HIWATT wrote:the first .047 should not be there. its a mod.
the JJ electrolytics are known for being brittle sounding too.

Thank you. Would it be safe for me to go ahead and cut that cap out to get it back to "normal"?

This being the cap in question:

that is the one.
the third one pictured is a .001 uf, .022uf is the typical value.
but get rid of the .047 first and this may also eliminate the popping.

I don't think it is the switch.

your board should be like this:

http://hiwatt.org/Layouts/Tag1.gif

I am not sure what that .047 cap was doing in there, but I cut it out and have noticed a pretty large improvment in sound. It definitely took some of the brittle sound out of there, very happy with that. The bad news is the pop is still happening, but it doesn't seem as loud!

The next time I have this amp to a tech for a bias or whatever I'm gonna have him replace that other cap you mentioned and then hopefully it will sound even better. This amp went from sounding "decent" to massive in about 5 minutes.

Do you know what kind of effect on sound that other cap you mentioned would be having? (The .001 uf that should be .022uf )

Thanks for your help DR.HIWATT, I truly appreciate it.

I don't think I would use the previous owner's tech, especially if he is the one that did the mod and the cap job.
can you find another?

Dr.HIWATT wrote:I don't think I would use the previous owner's tech, especially if he is the one that did the mod and the cap job.
can you find another?

I live in a different city from the previous owner so my usual tech will be looking at it!

Good!

Do you believe the .001 uf that is in place of the .022 uf would be having an inpact on the tone as well? I'm not sure which values do what.

Without doubt

Thank you for the info. I went and got the mid 70's layout from Hiwatt.org and compared it against my board just a few minutes ago. Would this also be a mod? And is that red wire supposed to connect there?