Ceriatone Chupacabra 50W: contemplating PT (power transformer) swap. What would I need to take into account?

[2dor]

So hear me out folks:

I got the Ceriatone Chupacabra 50W about a month or so ago and while I like the voicing on the amp, my curse is that I have two others (Molecular 50W and King Kong 100W) to compare it to

Having played them in quick sequence a few days back I couldn't help but notice that the Molecular and King Kong had a "faster" and slightly more pronounced transient response.
Now I know 100W vs 50W would be different but even between the Chupacabra and Molecular heads (both 50w) there's a noticeable difference.

Been reading up the interwebz (some Rigtalk, Metro, TGP posts) on these amps and it would look like that faster / bigger transient response could be due to the plate voltage on the power tubes.

If that's the case, it would somewhat add up:

- the Chupacabra 50W seems to have 420 - 435 VDC (haven't measured it yet; need to pull the chassis out sometime next week)
- the Molecular 50W has ~478VDC measured
- the King Kong 100W, per the manual, puts out 460 - 470 VDC

I went over the layout of some Ceriatone amps and see the Yeti 50W has a "better" power transformer than the Chupacabra 50W; "better" as in it has higher secondary voltage (350V vs 325V).

What would be my options to get that plate voltage higher if after the measurement it does show it's around the 420VDC mark?

If I grab a power trannie with slightly higher secondary voltages, would I need to mod anything else in the poweramp?

Asking because I do see slight differences between the Yeti 50W layout and the Chupacabra 50W in the power section (think that's a rectifier portion of the circuit) but even as the Yeti has higher secondary voltages, the manual says their (Yeti & Chupa) plate voltages are the same.

Anyway, the power trannies I found that seem to be close to "drop-in" replacements would be:

- Retroamplis JTM45 Reissue transformer (345/0/345)
- Mercury ToneClone P4550JT-G2M (360/0/360) harder to get here in the EU
- Hammond 291KX (seems like it can put out 353/0/353)

I understand voltages in these things can kill people if you're not careful etc. but moving past the "health & safety" stuff, is wiring up one of these the right way (following the layout and taps correctly) be enough to bump the plate voltages or would I need to tweak other things (filtering etc) in the amp?

Thanks folks & sorry about the wall of text.

 

[V|J]

Curious to read some thoughts on this myself.

 

[2dor]

@TheTrueZoltan! if they're still working on your order, maybe worth shooting a message to Nik asking they fit in the Yeti 50W power transformer instead or ask if they can do something else about raising those plate voltages; thing is, every forum thread I read, people seem to lean on higher plate voltages for high-gain amps for those tight / massive palm mutes.

 

[PatF]

For those transformers intended for a 50w Marshall it would just be a wire for wire replacement. Pay attention to the mounting hole pattern. The bolts could be a huge pain to get out and back in if they are under a board. Hopefully there are nuts between the chassis and transformer. If your filter caps are only rated for 450V, you should consider swapping for 500V caps. Check your bias too.

100W Marshalls have two caps in series for the first two supply nodes which doubles the voltage rating. It would also affect the attack some.

 

[2dor]

For those transformers intended for a 50w Marshall it would just be a wire for wire replacement. Pay attention to the mounting hole pattern. The bolts could be a huge pain to get out and back in if they are under a board. Hopefully there are nuts between the chassis and transformer. If your filter caps are only rated for 450V, you should consider swapping for 500V caps. Check your bias too.

100W Marshalls have two caps in series for the first two supply nodes which doubles the voltage rating. It would also affect the attack some.

Appreciate it, thank you.
Caps are all rated 500V and 600V and the PT is bolted to the chassis (nuts, bolts) and placed next to the board thankfully.
"Wire for wire" - that sounds good.

 

[James Freeman]

I don't think higher B+ by only 30-50v on plates will make the amp sound a whole lot different.
A Jose style preamp has low voltage diode clipping so raising the preamp B+ will not change the tone or feel that much.

 

[Achilles]

Why not ask the guy that designed the amp!
Nik is a gem when it comes to helping folks mod his amps.

nik@ceriatone.com

 

[2dor]

Why not ask the guy that designed the amp!
Nik walked me through a mod to my Ceriatone to mod the tone stack and bright switch.

nik@ceriatone.com

Thanks. Have since made contact with Nik about this and think we have a plan of action. I'll probably be doing the PT swap in the next month or two depending on how I get parts.

 

[Life Eats Life]

Transformer’s are much like a “ But’ Her ‘ Face
(A Butter’Face)
A whole lot more goin’ on then tappin’
that a** to account for in the equation man.
Naw, I’m just kidding, hell yeah, transformers make a huge difference.
But what difference will surface as components begin to seat?
Maybe too much bass or plate voltage/power tube changes..
It might sound TOO good?
It can be a lot of work getting the new change sorted with the older/other components and the amplifiers implemented design.
You could be stepping on your own d*ck.

I suggest Mega-research coupled with a faithful,good long Manson eyes stare down
in the mirror followed by sleeping on the decision and performing that Manson eyes stare down
when you awaken.
Then, make the decision
(LTFHOL!).

Hey man, you asked, I’ve done the power/output
change-out a few times, I get it.
I know that intersection all too well.
It’s a lot of effort and always a risk either financially/sonically/fatally.

I say, -Fire in the hole it, do it

 

[2dor]

Transformer’s are much like a “ But’ Her ‘ Face
(A Butter’Face)
A whole lot more goin’ on then tappun’ that a**
to account in the equation man.
Naw, I’m just kidding, hell yeah, transformers make a huge difference.
But what difference will surface as components begin to seat.
Maybe too much bass or plate voltage/power changes.
It can be a lot of work getting the new change sorted with the older/other components and the amplifiers implemented design.
You could be stepping on your own d*ck.

I suggest Mega-research coupled with a faithful,good long Manson eyes stare down
in the mirror followed by sleeping on the decision and performing that Manson eyes stare down
when you awaken.
Then, make the decision
(LTFHOL!).

Hey man, you asked, I’ve done the power/output
change-out a few times, I get it.
I know that intersection all too well.
It’s a lot of effort and always a risk either financially/sonically/fatally.

I say, -Fire in the hole it, do it

I hear ya. I've been slowly trying to learn board component names, have built some pedals and swapped pickups like crazy in the last 2 years or so.
Nik was kind enough to share some advice on the parts I'd need to change to get things right.

 

[2dor]

I don't think higher B+ by only 30-50v on plates will make the amp sound a whole lot different.
A Jose style preamp has low voltage diode clipping so raising the preamp B+ will not change the tone or feel that much.

My gripe isn't necessarily about the sound but more about the depth & snappiness of the attack I guess.
I'll try to get it done just because I need to get it out of my system now; knowing me, even if I try to shut it out * focus on other things, it'll still be there in a corner of my head itching me from time to time.

 

[Achilles]

knowing me, even if I try to shut it out * focus on other things, it'll still be there in a corner of my head itching me from time to time.

Brother from another mother.

 

[2dor]

Brother from another mother.

 

[Burger]

What value is the plate resistor on V1A, first gain stage? That layout says 470k, but check your actual amp.

 

[2dor]

What value is the plate resistor on V1A, first gain stage? That layout says 470k, but check your actual amp.

Thanks for chiming in Jason.
This is the pic I have from when I poked inside the amp a few weeks ago. Thinking about dropping that to a 330k?

 

[2dor]

Another one:

 

[2dor]

@Burger (Jesus I love this handle / nickname lol) it's definitely 470K

 

[2dor]

@Burger, @James Freeman looks like I'm off to a great start

I had the amp powered on, connected to my loadbox, all good & decided to measure Pin3 (plate voltage) on the EL34 tubes.

All good - got the reading but held the DMM too tight, hand slipped and I shortened Pins 3 (anode) and 2 ; saw a brief flare on pin 2 get no more plate voltage DC reading on them now.

Suspected I may have burnt the power tubes so I fitted new EL34 tubes into the amp.

No reading on pin3 unfortunately - pilot light does turn on and I do get readings on:

- both PT taps (3.15V)

- the 5V tap on the PT

- the HT fuse

- both AC secondary supplies from the PT:

Took the Mains fuse out, it checks for continuity (beeps) but I get no reading (AC or DC) while tapping its pins when it's plugged into the amp.

What else could I check or what would I need to look at next (aside from myself in the mirror and scolding)?

 

[James Freeman]

Remove power tubes.
Measure HT1 on reservoir cap after rectifier diodes while on standby.
Turn standby off, measure HT2 at the standooff post under rectifier diodes.

 

[2dor]

Thank you @James Freeman
HT fuse is shot - just took it out to look at it as well..