6550 OT Primary Z Question

[dorrisant]

I'm just wondering what the primary Z should be for a quad of 6550s. In particular, does anyone know of the measurements from the actual Dumble amps? Should I just used Ampeg values?

Forgot to add: I want to use a 400-0-400 PT.

[Roe]

At least 2k, probably more

[Guy77]

I'm just wondering what the primary Z should be for a quad of 6550s. In particular, does anyone know of the measurements from the actual Dumble amps? Should I just used Ampeg values?

Forgot to add: I want to use a 400-0-400 PT.

If you wanted to go with Ampeg values here is some info below.
Looking at these 2 sites for output transformers looks like they are between 1750 and 2900 ohms

https://www.tubeampdoctor.com/en/shop_O ... _VT_22_147

https://www.mojotone.com/amp-parts/Outp ... ansformer-

I had a 120 watt Ampeg VT -120 on the bench a few weeks ago and it had 485volts on the plates .




Cheers

Guy

[dorrisant]

Data sheet shows 3k5 @ 450v and 5k @ 600v. I was thinking half of the values for 2x 6550 since I was going to use 4x 6550.

[didit]

Hello —

A Dynaco a451 has 2.2K P-P. That is what is in the Winterland. A few threads here explore a bit. And that matches the datasheet.

Best .. Ian

[dorrisant]

That's it... the key words to search for to get to the Dumble spec. Dynaco OT and PT were in #0003 Winterland. I knew there was something about that around here. Funny, I have a local amp builder that has busted my chops on Facebook for using seasoned iron... I told him I had a set of iron from a Peavey Duece that I'd like to use and he laughed. HAD wouldn't laugh.

Thanks for the info guys!

[norburybrook]

That's it... the key words to search for to get to the Dumble spec. Dynaco OT and PT were in #0003 Winterland. I knew there was something about that around here. Funny, I have a local amp builder that has busted my chops on Facebook for using seasoned iron... I told him I had a set of iron from a Peavey Duece that I'd like to use and he laughed. HAD wouldn't laugh.

Thanks for the info guys!

both my amps built using Peavey iron are the best sounding amps I've made. You just have to use FWB rectification and you'll have around 500v B+


M

[didit]

Literally moments ago a Deuce set was delivered to the door. Voltage perhaps will be high at >600VDC, and with 3.3K P-P primary spec'ed. They look perfectly beastly. And what is the Facebook of which you speak? Sounds ugly and misinformed.

Best .. Ian

[dorrisant]

Only a fool would laugh at using that iron! FB is full of them most of the time.

[pompeiisneaks]

Only a fool would laugh at using that iron! FB is full of them most of the time.

FB is a hive of scum and villainy...

~Phil

[Tony Bones]

FB == Facebook? Last time I visited Facebook it was full of acrimonious political rants. Don't recall seeing any mention of Peavey transformers.

[pompeiisneaks]

FB == Facebook? Last time I visited Facebook it was full of acrimonious political rants. Don't recall seeing any mention of Peavey transformers.

Yes, there are many facebook groups for amps, and mostly full of pompous asses that dis on anyone that doesn't believe their magical invented prowess in amplifier design or tomfoolery. I used to participate quite a bit but after they degraded into constant flame wars I mostly sit back and eat popcorn. I'll occasionally chime in with props to a cool build etc. but otherwise, it's just madness.



~Phil

[Tony Bones]

Sounds like the old Usenet Newsgroups back before web browser based forums; rec.audio.tubes and alt.guitar.amps Everybody just pissing on each other, stinking up the place.

[Bombacaototal]

Reviving this old thread. I was checking the 6550 spec sheet on this thread and for class AB, two matched tubes and fixed bias the recommended primary at 450V is 4K. I am thinking of building an amp with 525V (plates) so a bit higher. But for a quad of tubes the primary at 450V is half = 2K. I am wondering if the primary should be something like 1.5K or 3.4K for the quad 6550 at 525V

[pdf64]

https://www.vtadiy.com/loadline-calcula ... calculator
I suggest that the full load supply voltages are used for loadline calculation, rather than the idle levels folk typically seem to have in mind.

The HT supplies used in valve guitar guiter amp can be anywhere between quite stiff and super saggy at the OT CT, even more so at the screen grid.