Tubes UP vs. Tubes Down

[DonMoose]

So, the majority of ODS builds are tubes down (fender/boogie style). If building a head, or rackmount, is there an advantage to tubes-down or is a tubes-up (marshall/hiwatt) build format gonna spoil the mojo?

[briane]

Ive built em both ways. They both work just fine.

tubes up is easier to make the cab, etc....

tube down gets amp hotter. While it wears the components harder, I believe it is the general consensus that these amps sound best when hot, and that is the reason the majority are tube down in my mind.

[DonMoose]

I believe it is the general consensus that these amps sound best when hot, and that is the reason the majority are tube down in my mind.

Good enuf, thanks!

[ic-racer]

Some of his larger amps, like the 300SL were tubes up. Perhaps he did not want to hang these massive transformers from the ceiling. I think those transformers are heavy, it looks like this amp has 2 or 3 carrying handles on top.

[Structo]

When you hang the tubes it helps the m0jo run into the tubes!

[briane]

Some of his larger amps, like the 300SL were tubes up.

good note. I have the parts for a full 300 watt SVT build from scatch, and no way I am hanging the 28lb OT upside down! (plus a 30lb PT) Also the heat from that beast would likely be enough to warm a small house in a nordic winter, so it will have a fan.

This amp will need casters, and possibly its own motor for powering around town

[marshmellow]

Heat = hot air is going to rise up. So, in a tubes down configuration, the heat emitted from your power tubes will heat up everything above them, which is your chassis. The problem is capacitors (and resistors to some degree) don't like that. It shortens their life time. You also get a change in capacitance/resistance related to the temperature. So just make sure your head shell is vented well if you want to do it that way.


The other problem, heavy transformers, has already been mentioned. Use steel or thicker aluminium and you don't have to care.

['67_Plexi]

Ive built em both ways. They both work just fine.

tubes up is easier to make the cab, etc....

tube down gets amp hotter. While it wears the components harder, I believe it is the general consensus that these amps sound best when hot, and that is the reason the majority are tube down in my mind.

With all due respect, that is simply not true or as we say in England, absolute bollocks

'Physically hotter' and 'harder' are two completely different things.
Generally you can run a 'tube up' amp harder and for much longer.
The big guy ended up with a corner in his amps thats hotter than the suns core, I don't think that was intentional and it seems a potential failure on his amps is ......the PT. Guess where that lives. Right there in hells corner.
This is even worse if someone decides to use a 4x6L6 PT for EL-34's. There are pictures around of an actual EL-34 ODS using a TF130 PT. Bet that got rather warm.

[DonMoose]

This is even worse if someone decides to use a 4x6L6 PT for EL-34's. There are pictures around of an actual EL-34 ODS using a TF130 PT. Bet that got rather warm.

That was going to be my next question - the twin PTs I see are spec'd for 7A worth of heater and EL34s want 1A6 each. That would put a quad at 6A4, leaving heater current for only two of the 2 12AX7s.

Did I miss something? Do the EL34 amps use different PT iron, or just run overspec? (gonna actually search that topic now) -- result: run a bit overspec; modern materials let you get away with it --.

(trying out a notation that abandons decimals for unit/decade letters - 6A4 would be 6.4A, kinda like 2k7 for a 2.7k resistor. Periods get easy to miss when I'm feeling my age)

['67_Plexi]

This is even worse if someone decides to use a 4x6L6 PT for EL-34's. There are pictures around of an actual EL-34 ODS using a TF130 PT. Bet that got rather warm.

That was going to be my next question - the twin PTs I see are spec'd for 7A worth of heater and EL34s want 1A6 each. That would put a quad at 6A4, leaving heater current for only two of the 2 12AX7s.

Did I miss something? Do the EL34 amps use different PT iron, or just run overspec? (gonna actually search that topic now) -- result: run a bit overspec; modern materials let you get away with it --.

(trying out a notation that abandons decimals for unit/decade letters - 6A4 would be 6.4A, kinda like 2k7 for a 2.7k resistor. Periods get easy to miss when I'm feeling my age)

You are correct, the TF-130 is not a good choice for EL34s. The HT winding isn't ideal for those tubes either. It gets bloody hot. I used one a long long time ago and ended up replacing it. HAD did use them on some EL-34 amps. I have heard from some sources that this part, which is still available from Magic Parts used to be a little stronger than the current ones available now, they may have even been made by a different manufacturer. The part number is a Magic Parts number, not a man. code so who knows. Magic Parts tell me they are made by the same OEM, but again, who knows.

My advice with most things in electronics, especially when you are dealing with high potentials is never assume the manfacturer built in a 'safety margin'. They may have done, but you might get the one part that's right on the limit.

I ended up getting some custom transformers built for a bunch of my early amps that had chassis cutout for laydown transformers.
After those were used up, I redesigned the chassis to use stand-up transformers and moved from a top mount to a bottom mount head design in the head versions. I also only make the top mounted OD2 combos in 50W versions and a 2x6550 version in the Tucana. The only exceptions are Bonamassas 100W amps, but they have PT designed for a 200W amp , forced cooling and a 1" air gap between the chassis and cab. They still get pretty warm running on full for 4 hours, but nowhere near that of other amps with the same config.

[AdrianJ]

Hi, newbie here trying to learn as much as I can about D-style amps before jumping in at the deep end with a Ceriatone kit and list of tweaks/mods..!!

As I'm considering opting for Nik's 100watt 4x6L6 model, I would probably er on the side of caution and install a cooling fan in the head. Could someone offer any advice on how I'd go about this - ie what kind of fan, powering it, placement etc...

Also, I'm insterested mainly in the clean side of the OTS and would be tweaking it as such - my thinking is that a 4x6L6 will give a warmer sound, am I right or would the 50W 2x6L6 version be just as capable? (FYI my eventual stage setup would incorporate a 50W OTS for OD sounds as well..!!)

PS: You build JB's amps?

[mike9]

How about tubes horizontal? The bugaboo with some combo's is the chassis and tubes both hang down. Hot Rod series, Bassman, etc. I'd like to build a combo chassis into a head, but in one amp I have no room on the top of the chassis to drill new holes for the tubes so they'd have to stick straight out the back. Makes for an extra deep head, but that's the trade off. Any disadvantage to letting them sit horizontal?

[Structo]

Hi, newbie here trying to learn as much as I can about D-style amps before jumping in at the deep end with a Ceriatone kit and list of tweaks/mods..!!

As I'm considering opting for Nik's 100watt 4x6L6 model, I would probably er on the side of caution and install a cooling fan in the head. Could someone offer any advice on how I'd go about this - ie what kind of fan, powering it, placement etc...

Also, I'm insterested mainly in the clean side of the OTS and would be tweaking it as such - my thinking is that a 4x6L6 will give a warmer sound, am I right or would the 50W 2x6L6 version be just as capable? (FYI my eventual stage setup would incorporate a 50W OTS for OD sounds as well..!!)
I think there is a thread where 2 hole vs 4 hole amps are discussed thoroughly.
Basically a 4 holer is going to give you more headroom but also just more girth to the tone.
I believe Dogears (Scott Lerner) likes the 100 watters more than the 50 watters because they simply sound better.
And with a master volume you will be able to tame the beast within.
PS: You build JB's amps?