Tube rolling with Quicksilver Mono 60s -- from KT77 to KT88? KT 120? etc.

Watch the highs on the GL KT88s.  The bass is good, but really tiring, harsh highs.  I tried them for close to 100 hours and gave up,  IMO they were never going to change enough to be keepers. My small tubes include many of the vintage ones mentioned above, for power tubes I roll el34s, kt 77 and TS 7581a. If you’re amp can use the 7581a give them a try first. Bargain price and an excellent overall power tube. Worth a try for a minimal investment.  Great base and mid-range, with highs that are extended without the harshness of the 88. 

@decooney
Thanks for the information. I wonder why the manual says that the KT88 can be used? BTW, I use the KT88 with my QS Silver 70 amps and Mike told me that can also use the KT 150 if I wanted to give them a try. This is from the M120 manual! Tube Complement 1 - 12AU7, 1 - 12AT7 2 - KT88 or KT150

@yogiboy
Not sure I’ve helped. Re-check with Mike for sure with your friend’s 120 amps. This is why I say to contact him, have your friend give him the serial# on the amps and ask again. I’m not sure if he tweaked the plate voltage up on mine at some point for the KT150s. Maybe your friend’s amps are okay with 88s. Yes, the "120" manual shows KT88s in two places, and I challenged him on that too. Note: check the front of the web page on the Mono 120s shows only this now "2 KT120 or KT150 outputs". KT88s are no longer listed there for Mono 120s. Manual needs updating, I don't know - better to ask mike on your buddy's version of the Mono 120s, mine are 2019 version. 

Yes, the older Silver 70, 80s, 100 amps seem to be fine to run the KT88s as I understand it, smaller transformers, likely lower plate voltage (supposedly). Same with hilde45s Mono 60s, ideal for KT88s, the sweet spot. I’d also buy a quad of KT88s right now if he’d say it’s okay for my specific mono 120 amps. I won't ask him a 4th time :)  

@glowworm -- harsh highs with GL 88? Whoa. I don't need that. Not just to play around.

It also depends on the amp circuit and what input/driver tubes you use.  

Since you know KT77s now and their signature in your amps, I think it's fair consideration, the highs could be a tad more tipped up (in your amps) particularly when compared to EL34s or KT77s. Always a tradeoff. 

My experience with Tube Rolling on my Monoblocks has been carried out by adopting a advice that was offered by a very experiences Tube Roller.
It was to get the Input Valves exchanged and a Type selected that is allowing the Power Amp to deliver a level of performance that is satisfying my personal preferences.

When this was achieved, the Pre Amp in use was seeming to be the next Device in use that was needing a Investigation.
The theory being that the Input Valves may benefit further from a different Pre Amp. 
The follow up investigations with Pre Amps has also produced a Pre Amp exchange, with the result being a Slagle AVC has been removed from the role of being the Systems Pre Amp.

I have been blown away by the impression the
Nelson Pass DIY Pre Amp has made on me, the Korg B1 is a superb 
device at a very 'affordable' cost, even if a Build Service is used to produce it, as I have done.

The Mono's Output Valves have not been Rolled, and there does not feel any immediate need to undertake this investigation. 
It seems hard to consider more can be achieved to the Measures already being perceived.
I am not shut of from from the idea of Rolling Output Tubes,
but there is a level of satisfaction in place at present, that does not feel it needs to be improved upon.

'All in' I invested about £700 in Tubes and Pre Amp, off which a proportion of the outlay will be recoverable if the unselected
Matched Vintage Tubes are resold. 

What ever the Brand of Monoblocks, I can recommend my experience with Investigations undertaken of addressing the Pre Amplification Delivery to the Output Valves, as a Method to produce a overall SQ that will be seen as very beneficial.
How such a approach will then interface with any exchanges of Tubes used at the Output, is at present a unknown, in relation to my experiences.