Help me mod my tube amp

Thanks everyone for the input so far. Several people suggested new tubes. As is probably obvious, I am pretty naive about tubes and open to your suggestions.

knotscottt: Yes, I run the amp in triode exclusively. I do not know whether the amp can use 12BH7a's rather than 12AU7's. I will try to find out.

russ69: I started using KT 120's all the way back when I bought the amp because I was coming from solid state and I was accustomed to bigger dynamics than the stock tubes provided. But I gather from your comment that KT 120's may be overkill?

johnss, sns, and viridian: Thank you for your specific recommendations. I will investigate options for upgrading each of the things you mentioned.

Bryon

Thanks, nlitworld, for those additional suggestions. I will check out the binding posts and wire you mentioned.

Mike B-- Thanks for your observation about the different directions this thread has taken. Both kinds of input are valuable to me. I've used Mullards (can't remember which ones) for signal tubes in the past with this amp and liked them. I think when it came time to replace them, I cheaped out. But I've been taking more of an interest in this secondary system lately, as I spend a lot of time in that room. So I will rethink my former frugality. To my knowledge, I have never heard Winged C 6550's. Do you have the same positive opinion about other 6550's?

Thanks also, Mike B, for the suggestions regarding resistors and capacitors. I have been internet researching potential replacements. Although I have modified preamps and speakers myself in the past, I am going to hire someone to do these modifications.

Hi all-- Update on this project...

My tech replaced the stock capacitors on the input stage of my Prima Luna Dialouge 4 amp with Dueland CAST PIO Hybrid copper/silver foil caps (matched pair). He also replaced the stock capacitors on the PCB board for the autobias circuit with V-CAP ODAM caps (matched quads).

Here is a pic of the internals before the upgrade. Here is a pic of the internals after the upgrade. The Dueland caps are the large red caps in the upper left and right of the image. The V-Cap caps are in the middle of the image covered in blue shrink wrap. 

Listening results: increased resolution, better soundstaging, and more natural tonality. 

I know several of you have made suggestions about upgrading the tubes. The GE12AU7 tested weak on the bench, so I have temporarily replaced them with Electro-Harmonix 12AU7. To be honest, I am somewhat overwhelmed by the options for tubes. I've probably spent 20 hours reading about various tubes, but I still feel poorly informed. I know that is my fault, not yours.

I am open to upgrading the amp further. If you have more thoughts, I am happy to hear them.

Thanks,

Bryon

P.S. The guy who did the work is Blackie Pagano. I have no affiliation other than this one service. What a nice experience. He was so knowledgeable, honest, and kind. He's in the LA area if you're looking for someone.

Hi John-- Several people suggested replacing the resistors, which I am open to, but have no experience with. Forgive the naive question, but do you know what parameters are important to match when replacing resistors? Obviously the resistance in ohms, but do I also need to match the power rating, max voltage, max temp, or other parameters?

Thanks, wharfy!

Update on this little project on my Prima Luna Dialogue 4 amp...

I upgraded the capacitors on the input stage with Dueland CAST-PIO Hybrid copper/silver foil caps. I also upgraded the capacitors on the autobias board with V-CAP ODAM caps (see attached pic).

Side note: The work was done by Blackie Pagano in Los Angeles. First time meeting him. He was great. Super knowledgeable, professional, and the quality of the work appears excellent.

Also, at the suggestion of several posters, I changed some of the tubes to NOS. For the 12AX7s, I added NOS Amperex with green labels made for Hammond Organ, purchased from Brent Jesse. For the 12AU7s, I added NOS Brimar from Upscale Audio.

And, at the risk of starting a war between Skeptics and Believers, I added a Synergistic Research Blue Quantum fuse on the autobias board.

The cumulative results are: better resolution, better soundstage, better tonality, and lower noise floor. Altogether, these were very worthwhile upgrades. I always have fun upgrading components and seeing (i.e., hearing) what happens.

I know I didn't do everything suggested so far on this thread. Please admonish me if I ignored your advice and you believe I would benefit from following it. I'm also open to any new upgrade suggestions for this amp.

Thanks,

Bryon

Thanks SNS. I read above that you upgraded the resistors in your PL amp. I bought this amp new around 2012. Can you tell from looking at the picture I attached whether the resistors are Takman or something else?

Bryon

Thanks, SNS. For the bypass cap, I think you're talking about the yellow cap marked "Swellong MPT 630V" in my photo. Is that right?

Hi tablejockey,

Here is the parts/labor cost rounded a little:

2 Dueland caps: $150

4 V-Cap ODAMs: $300

Labor for caps install by Blackie Pagano: $200

2 NOS Brimar 12AU7: $300

2 NOS Amperex 12AX7: $300

1 Synergistic Research Blue fuse: $60

Total: 1,310

Now that I'm looking at it all together, it sounds like a lot. But it really breathed new life into this 13-year-old amp. For some reason, I find upgrading existing things more rewarding than buying a new component.

Bryon

Hi sns,

Can you educate me... What benefits do people typically experience when they upgrade the bypass caps in the power supply?

Hi Jeff,

Yes, I did listen to the amp with the upgraded caps and the original tubes for a couple weeks. The most audible improvements were more organic midrange and sweeter high frequencies. I was happy with the changes.

Bryon

Let us know how it turns out, Jeff.