Twin > non-HRM conversion- now with a clip and pic

[Tonegeek]

Fired the Twin (actually Dual Showman)> non HRM conversion up last night. No smoke! There are a couple of things that I am going to look into tonight when I get home:

I am unable to get correct bias on the Winged C 6L6 outputs. 24 ma is the max current per tube I can get (@450 volts on the plate). I am using the bias tap, with 3k3>diode>10k pot > 27k > gnd. with tubes out the max bias voltage was -55. I did not check the adjustment the other way (which is the problem as I need less bias voltage than the adjustment allows) Seems I need to increase the 3k3 to something higher.

PI first measured 297v on the 110k plate resistor and 304 on the 120k resistor (backwards!). I swapped tubes and nothing much changed - WTF!. Then I adjusted the trimmer and and now it is measuring 300 and 292 respectively. More like it! I think the trimmer may have had some contact resistance on the wiper since it kicked in like that. I worked it back and forth and it seems ok now. (I of course will set the trimmer by ear when the time comes)

With a 150k FET sim. I get 204 on V1. I get 189v with a 100k FET sim. resistor across the V1 node. Regardless, the V1 plates are only about 3 volts less than V2. Dropping string is 2k2>22k>2k2 old style (non totem) cap PS. I want to get V1 down closer to 180v. I bet having and old RCA in V1 and a new EH in V2 is why there aint much diff in the voltage. Wish I had some more old RCAs.

dlator has ~241 or so on the follower plate and 215 on the recovery plate. I am coming off the screen node to 56k dropper for the recovery and on to a 75k dropper for the follower. Might try 47k in place of the 56k dropper.

I did not get to listen to the amp but may be able to tonight. Will post some pics and clips at some point.

[Structo]

I have had voltage swings as large as 15v before just with a tube swap on V1 and V2 so there is a lot of variability there.
Which makes it hard to figure out your dropping string.

I would continue to try tubes in V1 until you really like the tone you get on the clean setting, then play with the dropper.

You may have to play with the 22K and the 2K2 to get it where you want it.

On the D'lator your voltages look OK but verify that the cathode voltage on the follower is around 30v, that seems to be the sweet spot there.

[Tonegeek]

I have had voltage swings as large as 15v before just with a tube swap on V1 and V2 so there is a lot of variability there.
Which makes it hard to figure out your dropping string.

I would continue to try tubes in V1 until you really like the tone you get on the clean setting, then play with the dropper.

You may have to play with the 22K and the 2K2 to get it where you want it.

On the D'lator your voltages look OK but verify that the cathode voltage on the follower is around 30v, that seems to be the sweet spot there.

Exactly what I was thinking on the tube swaps.
I cobled this amp together with 4-5 jumpers in time for band practice last night and it did well. It is super quiet, no hum at all. The clean channel is really good (better than my BM, thanks to 100k plates!). OD got a quick setup and still needs a little more tweaking but was very useable. The amp makes a smooth transistion from clean to OD with no boosts on. It is a bit too middy with either PAB or mid boost on. With PAB and mid boost it sounds really fat. The mid boost relay sets the treble cap to either 258p or 1.2n.

One thing I don't understand is the last non-HRM I built was really smooth when playing double-stops ( E and G together on the G and B string). This one sounds about like my BM; I am getting a little disonance with the double-stops. It sounds like some lower frequency odd harmonics. My main motivation for wanting my own non-HRM was because I liked the way it handled double-stops compared to the BM/HRM version. I am baffled by what I am hearing. I always attributed the difference to the plate loads and now I don't know what is up since all my plates are 100k. One main difference with the previous non-HRM I built is (and I hate to say this) is the Mercury OT. It also had 15 volts higher on the output tubes due to using a Marshall PT. That amp sounded great right out of the chute. I remember it took me about 10 minutes to tweak it and it was done. I noticed the effect was worse until I got the bias up to where the tubes were drawing about 38ma each. I really need to get it even higher but need to rework the resistors in the bias circuit to get the proper range. Maybe that will help. I would post a clip to get help on this, but I don't think the mic will pick it up. I may try and see.

After playing for a bit with the FET sim resistor on, I took it off and like it better with the higher voltage, at least at practice. It just seemed a bit clearer.

I know my tubes need to be swapped. I think the RCA needs to go in the PI. I may just pull the pre's from my BM and put them in the same slots in the new amp.

[Tonegeek]

I am tweaking this thing and I don't remember the first non-HRM I built giving me this kind of trouble. It sounds pretty good with just OD on but it is like a wah-wah (bunch of mids) with PAB or mid boost. I think that may be normal for a non-HRM but I need some other opinions. If I use PAB and mid boost then it is pretty fat again but too loud compared to them being off, but individually it is poop unless you are doing SRV then it may be OK.

I did put the RCA in the PI and the two new EH in v1, v2. Now my voltages are about 7 volts apart from V1 to V2. and with the 120k FET sim resistor I get 183 on V1, so I got the voltage in line. Got 30 volts on the follower cathode as suggested. I played some with the PI trim and OD trim and the amp has no trouble going into feedback. Also the double stop thing is not as noticeable with just OD so I am happy about that. Just wondering what to do with the PAB and mid boost. I do have provision for the mod where when you switch to PAB you also switch a cap across the bottom of the treble pot and the plate resistor. This sounds about like having PAB and mid boost on at the same time. Not too useful as it is also a large gain boost.

The circuit is similar to #124 but I have a .02 for the V2a coupler and a .01 on the PI input. I have tried the stock setup and it was too thin in OD and too boomy in clean. This was the same issue on my first non-HRM build and swapping the 2 caps fixed the issue. Seems that is working here as well. Ok, so I need some ideas about tweaking the mid boost and PAB.

[ic-racer]

I don't know if you saw this older thread. I got a fantastic result from my Super Twin conversion.

https://tubeamparchive.com/viewtopic.ph ... torder=asc

This is the final schematic I wound up with: https://tubeamparchive.com/files/final_ ... ic_594.pdf

[Tonegeek]

I don't know if you saw this older thread. I got a fantastic result from my Super Twin conversion.

https://tubeamparchive.com/viewtopic.ph ... torder=asc

This is the final schematic I wound up with: https://tubeamparchive.com/files/final_ ... ic_594.pdf

I reread that thread and you got really good results judging by the clips. I thought of doing reverb, but a loop is more useful to me so I did a built in d'lator instead. I debated keeping it a combo, but decided against it, so it is going in a head cab. One questiong, can you hear the difference between the 22k and 33k inputs shown on your schematic? I experimented with useing a Fender style Hi/Lo input but decided to go with just the 33k input instead.

I played the amp a lot tonight and am starting to find the sweet spots. My OD channel is slightly thinner sounding than the clean channel so I need to balance it a bit. My goal this evening was to just get the voltages in line which I mostly did. I can't decide if I like V1 at 180 volts or at 200. I need to crank the amp to figure that out. At low volume it all sounds good.

[Tonegeek]

Fixed most of my issues, got my voltages where I want them (except I am still experimenting with V1-V2 but it is close. Heres a clip and a picture:

[Bob-I]

Sounds good to my ears!!

[topbrent]

Sounds good man!

[bluesfendermanblues]

Sounds really good, nice compression, perhaps a bit dark - what snubber values are you using.

[Tonegeek]

Sounds really good, nice compression, perhaps a bit dark - what snubber values are you using.

One of the jumpers hanging off in the picture is to the snubbers. Currently I have 270p on the first OD triode and 330p on the second. I still have some tweaking to do because the amp sounds a lot different cranked up than it does at low volume like when this clip was made. It gets brighter as I crank it up. If it did not get brighter, I would throw a bright cap on the master to make t a bit more crisp. I am working with the voltage at V1, the snubbers, and the OD treble bleed circuit to find the right balance for the highs. Lower plate v mutes the highs a bit but sweetens the harmonics. Higher v has the opposite affect. I like the lower v for the clean mode, but the higher v is firmer with OD, hence the balancing act. I will post some more clips with the amp cranked when I get a chance. My goal is to get the amp sounding mostly like it does now, only at a higher volume.

[mat]

Sounds really good to me, congrats !

[Bob-I]

I still have some tweaking to do because the amp sounds a lot different cranked up than it does at low volume like when this clip was made. It gets brighter as I crank it up. If it did not get brighter, I would throw a bright cap on the master to make t a bit more crisp.

Well first off, my impression is that this is the reason for the bright cap, adding brightness at lower volumes to offset the lack of brightness at low volumes.

Second try bringing the master volume up to about 11:00 and dropping the overall volume with the D-ulator return. It will get the master volume up to a level where it won't rob highs as much.

[Structo]

Second try bringing the master volume up to about 11:00 and dropping the overall volume with the D-ulator return. It will get the master volume up to a level where it won't rob highs as much.

Yes, this is the way I do it as well, I set the first volume about 11 o'clock and the master around 1 o'clock then control over all volume with the D'lator output control. Adjusting the return as needed when turning up.
Seems to sound the best

[odourboy]

I like it Whit!