need help choosing trannies for future builds...

[flood]

hey there all,

i'm going to take the excellent advice of the resident gurus here again: i've built two amps so far and am working on a third. the two so far include a firefly (pics over at http://rsjonline.com/forum/forum_posts.asp?TID=2825) and the TW/vox/allen inspired 6v6 SE amp (still troubleshooting, pics up soon) that is the subject of this thread: http://ampgarage.com/forum/viewtopic.php?t=6696.

i want to build a couple of 18 watters - a 2061x as well as something with a lot more preamp gain - i'm thinking along the lines of a soldano atomic 16. since i live in india, ordering transformers is a bit of a hassle, and i get mine custom wound locally. my questions:

1. what secondary voltage would i need to specify if i want about 320V on the EL84 (or maybe 6v6) plates? i was thinking 275-0-275, but that struck me as a bit too little - would give me only about 300V after rectification, filtering and loading, i think?

2. if i decide to use 6V6s instead, can i still stick with the same OT (8k CT primary, 0-4-8-16 secondary)?

3. what does a hybrid rectifier sound like? e.g., an EZ81 whose diodes are bypassed with say UF4007s for more power?

right now i'm thinking of ordering:

PT: 275-0-275 150mA (in case i want to add more preamp tubes - would the current be enough for 2 EL84s and 4 ECC83s?)
3.15-0-3.15 5A (for the lulz , in case i decide to use an EZ81 in either amp)
27V 30mA (bias for the atomic 16)

OT: EL84 P-P 8k CT, 0-4-8-16, 25W (i overspec everything, as far as possible...)

steel used will be CRGO.

thanks to all in advance!

[flood]

bump.

[morcey2]

hey there all,

i'm going to take the excellent advice of the resident gurus here again: i've built two amps so far and am working on a third. the two so far include a firefly (pics over at http://rsjonline.com/forum/forum_posts.asp?TID=2825) and the TW/vox/allen inspired 6v6 SE amp (still troubleshooting, pics up soon) that is the subject of this thread: http://ampgarage.com/forum/viewtopic.php?t=6696.

i want to build a couple of 18 watters - a 2061x as well as something with a lot more preamp gain - i'm thinking along the lines of a soldano atomic 16. since i live in india, ordering transformers is a bit of a hassle, and i get mine custom wound locally. my questions:

1. what secondary voltage would i need to specify if i want about 320V on the EL84 (or maybe 6v6) plates? i was thinking 275-0-275, but that struck me as a bit too little - would give me only about 300V after rectification, filtering and loading, i think?

2. if i decide to use 6V6s instead, can i still stick with the same OT (8k CT primary, 0-4-8-16 secondary)?

3. what does a hybrid rectifier sound like? e.g., an EZ81 whose diodes are bypassed with say UF4007s for more power?

right now i'm thinking of ordering:

PT: 275-0-275 150mA (in case i want to add more preamp tubes - would the current be enough for 2 EL84s and 4 ECC83s?)
3.15-0-3.15 5A (for the lulz , in case i decide to use an EZ81 in either amp)
27V 30mA (bias for the atomic 16)

OT: EL84 P-P 8k CT, 0-4-8-16, 25W (i overspec everything, as far as possible...)

steel used will be CRGO.

thanks to all in advance!

1. 275-0-275 will give you around 340V after rectification/filtering/loading with an EZ81 rectifier.

2. Same OT will work great with 6V6s.

3. I've never built a hybrid rectifier with paralleled diodes and from my limited understanding it wouldn't work the way you think it would. I've done many switchable SS/valve rectifiers and it can be handy for different types of sounds (sag v. no sag), but I don't think paralleling them would have a significant effect. One of the diodes would do all the work and the other would sit there wondering when it would get in on the action.

The PT that you spec'd would be fine and should handle 2xEL84(or 6V6) and 4xECC83 quite nicely.

The OT is a little more complicated. There's interleaving and stuff like that to think about. Stuff that's way over my pay grade, but what you've spec'd there should work fine.

Matt.

[flood]

thank you very much, matt, that helps quite a bit.

the people who are winding my transformers have been in the business for quite some time and if i understand correctly, have a lot of knowledge regarding the winding of OTs for all sorts of power stages... the woman who winds the trannies has being doing it since she was a kid, i assume. i don't understand much of it, so i just leave it to them. they have built some Pts and OTs for me in the past, and they work pretty good so far. and are very cheap to boot! living here definitely has some advantages.

i'm also going to contact another manufacturer who built some excellent toroidal OTs for me once and ask them for tranies of the same specs... that way, i know which one is better for future builds.

will post pictures of the build(s) in progress, and promise to do a neater job than on my previous builds! thank you for the help.

[flood]

hey all,

sorry to revive this thread again, but i thought i should double check before commencing on my next build and order.

a friend has commissioned an amp build from me. he wants a cleanish sound that can get nice and gritty too, with a fair amount of tonal flexibility. he would like to achieve a good driven tone without using any pedal distortion and is averse to heavier sounds.

after the (surprising!) success of my first original design (sorry, have been slacking on the photos and clips - work has been rough of late), i thought about thinking of a new one again, along the lines of vox and fender (and i believe Dr. Z or divided by 13 had some similiar aspects? cant remember now) . the topology i have planned out is:

- 2 input stages - bright triode (1/2 12AX7) and bight/dark adjustable pentode (6SJ7)
- a switch that lets you select between each channel discretely, or both channels with the input links or the triode channel cascading into the pentode channel
- a cathode follower (marshall values, probably, maybe 56k instead of 100k to reduce the overall gain) and marshall tonestack, master volume.

now comes the big question -

i wanted to design an end stage that is as flexible as possible. as i am ordering a custom wound transformer, specifications can be met easily.

i want the power stage to accept any of the following tubes:
-EL84 (noval socket will be wired in parallel)
-6V6 and variants (6F6, 6K6 etc.)
-6L6
-EL34

from my experience with my last build, EL34 does not work with a 5k output tap (i used a 6CA7 and smelled heated plastic, so i turned off the amp immediately - no damage was done). my last build involved a 5k:8E OT, and a 470R cathode resistor.

so this time, to eliminate any chances of frying something, i've decided to order the OT with the following specs and use a DP4T switch to change he primary as well as the cathode resistor (of course, only when the amp is turned off!):

Primary:
5k-4k-2.5k-0 (EL84/6V6-6L6-EL34 respectively?)

Secondary:
0-4-8-16 ohms
Power Handling: 15W

the PT will be: 250-0-250, 100 mA and 3.15-0-3.15 3A

will these specs be ok in your opinion for running even a 6CA7 in full tilt (which i doubt will ever happen, seeing that the man is more of a bedroom player)?

thanks to all in advance... again!

[flood]

bump

[flood]

ok, i checked out some other forums, and it says that an EL34 SE in class A should see a primary of at least 3k on the OT. 5k would give it better results.

is this correct? am really confused now, have seen different things everywhere. would 5k-4k-3k-0 be overkill? i think i will order it anyway, seein that it can't hurt to have a tap or two more. thanks anyway!