Fender 5D5

[StevieRayVehkakoski]

Just saw this on youtube:

This is pretty much the sound I've been hearing in my head for quite a while and I guess I should give it a try.

I assume the amp on the video is this:

http://www.kbapps.com/audio/schematics/tubeamps/fender/pro5d5.html

I've got these transformers:
 - 280-0-280 / 200mA power with 5V/2A tap
 - Hammond 1645 OT (30w,5k)
 - Hammond 193H choke (200mA,5H)

So, with a GZ34/5AR4 I should get about 350-360V B+ which is a bit low but I guess it should be ok. Unfortunately I can't use 5U4G as I've only got 2 amps of 5V plus B+ would drop too low anyway. What do you think, is this going to affect the sound or the dynamics significantly? I guess the the5U4G would SAG way more than the GZ34/5AR4?

What do you think of the PI, I guess it's a paraphase but the signal to the second grid is taken from a bit strange place, 270k/220k and 50k to ground? Does this sound right?

The inputs, the 100k for 2 triodes and 470k on cathode for 4 triodes equates to 200k/1,8k for one triode?

[tubeswell]

Should still work okay with the 280-0-280, but it will sound 'dirtier'/warmer. You may want to go to 220R (or even 180R?) cathode resistor possibly, just to get the 6L6s sounding good (which of course will mean the plates will be running around 300 I guess, but it should still sound okay like that)

Edit - you could use that 280-0-280 PT with SS rectification and make a '66 Supro Tbolt FWIW

[tomcatarnold]

Ideally that PT would be a better fit for a 4xEL84 based power section, but it'll work if you're OK with end result volume/headroom being that of a 2x6V6 based amp.  If I were going to gig with it in a medium sized club with a moderately loud drummer unmic'd, I'd want 380-400ish vDC on the plates of the 6L6/5881's.  Also, IMO, even if you could, using a 5u4 rectifier will drop to many volts to practically use with 6L6's/5881s.

That Pro in the video sounds really sweet with single coil pickups, but it would be a different story with anything in the 8K+ territory (for example PAF h/b's and hotter, P90's) with the stock circuit (IMO this is true for most tweed circuits).  To give yourself some pickup type versatility, I would split the V1 cathodes and bias one of the triodes/channels with a 2.2K/.68 or 1uf bypass cap and play your hotter pickup guitars through it.  To match the stock configuration bias the other triode with a 1.5K (1.8k would be fine too)/5+uF combo. All this assumes a 12AY7 in V1 and I would stick with 100K plate resistors...  especially considering the PT is running B+ 50-60V less than the stock Pro design.  

The paraphase PI is a big part of 'that' sound and the way the amp responds, so I would stick with it

[StevieRayVehkakoski]

Right now I'm playing with a 5Y3-rectified 6V6 push-pull amp with about 310V B+ and I've got plenty of volume but the bass starts to fart out pretty bad and the dynamics suffer a bit although I like the natural compression of the amp.

So, In real life with this 280V PT and a 5AR4/GZ34 I would have something like 370V B+? And with cathode-bias I would have about 330-340V plate-to-cathode. Has somebody experimented with different voltages on 5881/6L6-tubes, I'm looking for soft and warm and saggy sound for 50's kind of jump-blues / jazz stuff so I guess my voltages should be about right?

About rectifiers and sag: The 5D5 uses 5U4G which sag way more than the 5AR4 under load, what's the experience is this generally notable? As said, I really like the soft, saggy response but the 6V6:s just fart the bass too early and I've got some Jensen EM1500-speakers that I love but the 6V6:s just don't seem to have enough control on the cones.

[tubeswell]

So, In real life with this 280V PT and a 5AR4/GZ34 I would have something like 370V B+?

Yep take a look at the brown (6G9-B) tremolux/vibrolux circuits - they use that sort of PT and get those voltages

And with cathode-bias I would have about 330-340V plate-to-cathode.

Or even around 300V I reckon - depends how hot you bias the 6L6s

About rectifiers and sag: The 5D5 uses 5U4G which sag way more than the 5AR4 under load, what's the experience is this generally notable? As said, I really like the soft, saggy response but the 6V6:s just fart the bass too early and I've got some Jensen EM1500-speakers that I love but the 6V6:s just don't seem to have enough control on the cones.

Depends on the amp - I've got a 5G9 (5U4G with 6V6s) and the sag and bloom is really nice under load - but I am running a 5k Pr OT on that - I reckon 8k would be too mushy.

6L6s can sound really nice at lower voltages and you don't have to run them hot either. Here is a link to a clip of a cathode biased SE 6L6 running at about 330 with 290 on screen and 43mA tube current (excuse the trem). (Cathode voltage was 20.6 with 472R Rk). Speaker is a Celestion G10. (The PT HT winding is 280-0-280, and teh rectifier is a 5U4G I hasten to add, so expect even lower voltages with 2 x 6L6).

http://music-electronics-forum.com/attachments/12710d1297150553-super-ac4-g10-6l6-5u4g-lo-ht-trem.mp3