anyone running 6550's in a rocket?

[lumox0013]

im getting geared up for a rocket build i want to use 6550's this time,just thought some of you might have some tips. In particular what output trany specs i might look out for and what are your experiences with cathode biasing on 6550's? any input greatly appreciated, thanxx guys

[RJ Guitars]

I built my original Rockster (octal Rocket) amp with the thought that I would use a pair of 6v6's. However, I soon found that KT66's, 5881's, EL34's, etc sounded great (better than the 6V6 tubes - YMMV), each in their own way. I tried a pair of NOS GE-6550's in it but I wasn't impressed enough over the tone of the KT66's to tweak it for those tubes. I also was worried about them running too hot because the original build was in an Express chassis.

Now I've got a bigger chassis going now with still bigger iron and plan to run the voltage up and really make some noise. It sounds like you might get this done long before I do so I'll be curious to follow along and see what you think. Would also be curious what B+ voltages you are going to run.

rj

[Zippy]

Would also be curious what B+ voltages you are going to run.

Ditto that. What are your goals - do you intend to run the 6550 at full power or follow from the Express design (and some of my own preferences) and run the large tubes at the lower end of their voltage range?

Regardless, I suggest that you mind the dropping string to keep the rest of the voltages at original Rocket voltages.

[lumox0013]

I have a power trany and choke from an old milltary chassis its running 375-0-375 unloaded so not going to blow them out, plenty of filament power though. as far as what I'm trying to acomplish I play with a lot of pedals looking for more headroom,bottom end, faster attack. I love my el84 rocket and want to run another amp in parallel. have built several octal-rockets w/5881s,el34s, they seem to bee lacking so i thought id try some 6550s i dont want it hifi type clean more like hiwatt clean. im thinking one of the keys will be the Output Trany.wanted to keep the cathode bias but am lost as to how to adjust for 6550s @ 525v. any input would be greatly appreciated as always. cheers lumox

[M Fowler]

https://tubeamparchive.com/viewtopic.ph ... b21140a982

[M Fowler]

https://tubeamparchive.com/viewtopic.ph ... 30d8a41577

[Zippy]

I play with a lot of pedals looking for more headroom, bottom end, faster attack. I love my el84 rocket and want to run another amp in parallel. have built several octal-rockets w/5881s,el34s, they seem to bee lacking so i thought id try some 6550s

Have you determined where the "lack of headroom" is occurring? Given the low voltage of V1, you may reap considerable benefits from restructuring your dropping string. On the other hand, if you keep the pre and PI as-is and boost the output power, you may get no perceivable benefit unless you start running the preamp differently.

[RJ Guitars]

I play with a lot of pedals looking for more headroom, bottom end, faster attack. I love my el84 rocket and want to run another amp in parallel. have built several octal-rockets w/5881s,el34s, they seem to bee lacking so i thought id try some 6550s

Have you determined where the "lack of headroom" is occurring? Given the low voltage of V1, you may reap considerable benefits from restructuring your dropping string. On the other hand, if you keep the pre and PI as-is and boost the output power, you may get no perceivable benefit unless you start running the preamp differently.

Yeah this is a good thought. There are a few guru's who believe that ken Fischer really got the voltages right on these first three tubes and that is key to the magic. I have not experimented with that so much myself so i can't add any data to one side or the other of the discussion, but I would like to know what other folks have found.

rj

[lumox0013]

mark- thanx for the heads up i thought I heard you mention you were running 6550s I would have found the thread eventualy but its hard to run down the right ones when you have several thousand. did you ever switch yours up to the fixed bias ? curios because I thought that would make quite a change in the overall feel.

zippy-good question I really dont want to change the overall tone just to add to it, more punch and clarity on the low end side without messing with the compresion and sparkle up top I thought the key would be in the power section. if you have any sug. on adjusting the pre I will give it a try on my existing octal rocket,currently running 6l6s.I changed the plate res on v1 to 150k I thought it detracted from the sound(opened it up kind of like a fender) I'm not in the know enough to mess with the topology. I'm collecting parts for a dumble but feel I have a long way to go before I get there. still practicing!

thanxx for the responces this place is the greatest. I think I found a suitable OT on ebay waiting to see if I can score it for a reasonable price. cheers

[M Fowler]

The amp sounded so good I didn't want to do anymore work to it. Not sure if I could even duplicate my own amp, that is how much I like it.

Now that I have time, I want to setup some recording equipment and post.

Mark