Real 5881s

[Blackburn]

Okay I've been looking around trying to get a feel for what to do with my original Tung Sols. The tweed Bassman seems to run them around 430 to 450 on the plates and I've heard other reports of the early 60s Fenders running them much higher. I'm not at all interested in getting as much volume or headroom as possible, simply tone. When I mean tone, I usually mean distorted tone, but clean tone too. I don't care for harsh highs and keep my treble or cut controls down usually, depending on the tubes I'm running, another reason to bring down the plate volts. The main reason I'm posting about this subject is I want to know if anyone has had any luck running theirs around 375 to 400 on the plates. I'm almost positive I'll have around 375 with a 5AR4 and the latter with a drop in SS rect. My PT is 315-0-315. I'll be rolling a lot of different types of output tubes simply because my OT is very flexible and I have much curiosity. Should I send back my PT for something with a higher B+ or should I make with what I have now? What do you guys think?

David

[tubeswell]

Russkie 6P3Se are 20W tubes that can easily take 450 on the plates.

[Milkmansound]

I use the 60's Tung Sol 5881 in my amps as often as I can. What a great tube.

Its pretty forgiving - I bet plate voltage under 400V does not make much different.

Just try them!

[David Root]

I run a pair of NOS Tung-Sol 5881s in my low power tweed twin build at ~415V and 35mA cathode draw. Sounds utterly authentic!

[Blackburn]

I run a pair of NOS Tung-Sol 5881s in my low power tweed twin build at ~415V and 35mA cathode draw. Sounds utterly authentic!

I like the way that sounds! Everyone, thanks for all the input. But David, what's the secondary coming off your PT and what's the B+ out of your rect? My problem is I don't think my B+ will get that high with 315vac into a 5AR4. I'm pretty sure I'll only get up to 415 with a SS rect. I would really love to be able to hold on to this thing and not have to wait a couple weeks and go through all this with MM. I'm getting more and more tempted every day to just build.

[rp]

My 5F6A clone and 5C8 clones have 325 & 300 Vac secs, the 5F6A has 50/50 32/32 caps, first is around 420V, the other ~390V on the plates at around 35mA with NOS 5881. The 5F6A has a cathode bias / fixed option. Both sound rich and wonderful. My fave tube I think. So, given my limited experience, you can't go wrong w/ 390-425v plates w/ NOS Tungsols.

[Blackburn]

My 5F6A clone and 5C8 clones have 325 & 300 Vac secs, the 5F6A has 50/50 32/32 caps, first is around 420V, the other ~390V on the plates at around 35mA with NOS 5881. The 5F6A has a cathode bias / fixed option. Both sound rich and wonderful. My fave tube I think. So, given my limited experience, you can't go wrong w/ 390-425v plates w/ NOS Tungsols.

Okay, that's cool... But are you using a 5AR4 for rectification? If so, what brand, and old or new? I'm now wondering if the brand of tube can make a drastic difference in how much DC it rectifies. My AC30 build has 260 in and out of a real Mullard I only get 310vdc. Not that I want more than that for that amp, I just assume it will be similar with the 5881s. Is there a technical aspect I'm not grasping here?

[rp]

Mullard 5AR4 & GE 5U4GB for the 5C8. That 260V is low for EL84's IMO so 310V sounds about right. IME 280-290V Pts will give ~330-340V with a Mullard 5AR4, which is more common for Voxes and other EL84 amps. But I bet Voxes when wall voltage were lower probably had ~300V on the plates. I wouldn't worry much. Only way you are going to get them higher is to change PTs. Even a SS rec won't give much more than the Mullard, in my 5F6a there's hardly a difference. BTW those sec voltages I gave were unloaded, that will always screw you up. Some PTs will show little difference btwn loaded and unloaded too depending how big and well regulated they are. I gave up on the math and rectifier voltage drop charts and just go by feel now, I've actually had better luck that way.

[Blackburn]

Actually the PT for the AC30 is not the same one I'll be using for this amp. I was just referencing the rectifier, which I have two of, one for that one and another for the 5881 amp. My sec is 315-0-315 for this one. I didn't know those were your unloaded values. I guess you're seeing a good deal lower than 400v loaded then, no? There's a pretty big difference with MM trannies between loaded and unloaded. I think I remember seeing as much as 60v difference with my 5B6 using the 5U4GB.

[David Root]

I think my 5E8A PT is a Mag. Cpts. tweed bassman, 40-18073. This is rated 325-0-325 @200mA load. So it is probably 330-0-330 or higher at idle. I used two 5R4G rectifiers which drop about 50V. They sound noticeably better than 5U4G, it's not subtle.

I don't know if 315-0-315 unloaded will cut it thru a GZ34. If your target is 400V @ idle thru a GZ34 you just might make it. For comparison I used in my Dumble Bluesmaster build a MM low voltage tweed Bassman PT, 310-0-310 loaded. No tube rectification but I get about 420V plates at idle on FOUR 6L6GA. So that would increase a bit with only two power tubes.

[Blackburn]

The figures I stated are loaded. I always see and I mean ALWAYS see the figure they say, plus or minus a volt or two when everything's up and running. Very high quality trannies, in my opinion. With a SS rect I'm sure I'd be above the 400 mark, but I do want to utilize my 5v filament taps. I've not used them in the past and I have seen my other sec taps go up a bit, such as my 6.3v heater string. I have dropped in the SS cap before so that's always an option, but I currently have a Mullard 5AR4, Tungsol 5V4G, and the largest coke bottle I've owned, an RCA 5R4GY, which must be the most masculine tube in existence, all aching to be a candidate. The weather is SO beautiful today, I'm debating whether or not to start drilling the chassis right now!

[rp]

To sum up, 325-330Vac unloaded 200-300mA PT with a 5F6A/JTM45 power string w/ a Mullard 5AR4 should get you from 390-420V on the plates with NOS 5881s. What's nice about ~400V is you can brown it out with a 5U4 or punch it up with a SS plug in thingy, or even play around with 6V6s. Get a PT with 3A on the heaters.

[Blackburn]

To sum up, 325-330Vac unloaded 200-300mA PT with a 5F6A/JTM45 power string w/ a Mullard 5AR4 should get you from 390-420V on the plates with NOS 5881s. What's nice about ~400V is you can brown it out with a 5U4 or punch it up with a SS plug in thingy, or even play around with 6V6s. Get a PT with 3A on the heaters.

Thanks, man. I guess I'll get to work then!

Forgot to mention I also have a couple 5U4s and those 6L6GCs from my 5B6 that is no more. So many options! I have a feeling this may be my favorite amp soon.

[Diablo1]

I built a bassman 5F6A clone from a Weber kit. The PT voltage is 360-0-360 VAC, and this gives 462 volts DC with a 5U4GB rectifier. It uses NOS Philips 6L6GWB (5881). I'm happy with the way it turned out.

[IMG768]http://i268.photobucket.com/albums/jj29 ... G_0344.jpg[/img]

[Blackburn]

Are those black beauties in there? Whenever I see someone use caps that aren't of the norm I get extra curious...

Clips!