Holland Amp

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sonicmojo
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Holland Amp

Post by sonicmojo »

I run across odd amps a lot. This is a Holland Amp from 1998. I guess the company ceased to exist in the early 2000s. The numbers have been scratched off the transformers and there are a lot of scribbles on the chassis. It's got some issues with grounding of the pots that I need to sort out probably due to oxidation of the super thick aluminum chassis. I'll probably place in a buss bar for better longevity. Has anyone drawn up or have a schematic of this amp?
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Last edited by sonicmojo on Sun Nov 12, 2017 9:52 pm, edited 1 time in total.
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Bryan
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sonicmojo
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Re: Holland Amp

Post by sonicmojo »

I'll forget finding any schematic on this. The customer just told me he had this built in 1998 as a custom clean jazz amp. It is probably a lot like a Little Jimi but dialed back. Has 5751 tubes in a couple positions as well which makes sense for more clean headroom.
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sonicmojo
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Re: Holland Amp

Post by sonicmojo »

Well I went ahead and traced this amp out as it might come in as handy reference for someone in the future. I do like the reverb on it. It has an interesting layout placing the reverb circuit as far away from the power section and transformers as possible and some off axis preamp tube sockets, assuming for lowest noise possible. I didn't like the grounding of the pots to chassis as the oxidation over the years got in the way so I changed the front preamp grounding scheme to a common ground point. I couldn't use a buss bar as the pots were too close to the board but ran wires instead. There are a lot of other galactic points in the amp but it is very quiet.

I guessed on the under board jumpers so if anyone sees something that might be missing, please let me know.

Thanks!
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joeboo88
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Re: Holland Amp

Post by joeboo88 »

Thanks for doing this Bryan.
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sonicmojo
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Re: Holland Amp

Post by sonicmojo »

I was playing around with the amp today and you can get only reverb if you turn volume all the way down, a la Silvertone 1484 type thing. But as you turn up the volume, the reverb backs down but is still fairly deep at higher volumes if you keep the mix high.
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mojotom
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Re: Holland Amp

Post by mojotom »

Thanks !
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sonicmojo
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Re: Holland Amp

Post by sonicmojo »

Can someone tell me the purpose of the 47pf capacitor between pins 2 and 3 of the first preamp tube on this amp? I assume it is to roll off some reverb highs and prevent any oscillations. I have a second similar Holland amp on my bench now that has a 100pf capacitor between pins 1 and 3 of this same socket. Something tells me that one of these is incorrect but both amps work.
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martin manning
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Re: Holland Amp

Post by martin manning »

In the first case it would be a treble bleed, shunting a dB or so of HF above 10kHz from the input to the cathode. In the second case the cap is a "snubber" to roll off ~4dB above 10kHz, similar to bypassing the plate resistor with a small cap. Both may be correct.
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sonicmojo
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Re: Holland Amp

Post by sonicmojo »

martin manning wrote: Mon Dec 04, 2017 11:38 pm In the first case it would be a treble bleed, shunting a dB or so of HF above 10kHz from the input to the cathode. In the second case the cap is a "snubber" to roll off ~4dB above 10kHz, similar to bypassing the plate resistor with a small cap. Both may be correct.
Thanks for the explanation Martin!
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sonicmojo
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Re: Holland Amp

Post by sonicmojo »

....and upon further testing, I certainly hear that a lot more of the reverb highs are rolling off on this amp but it has been a few weeks since I listened to the last Holland. The reverb does not sound nearly as nice as the other to my ears. The board layout is pretty much the same, but some different plate resistor values in the reverb circuit, higher values on the dropping resistors, and slightly different value pots, It also has a different single 8 Ohm output transformer - once again all transformer identifiers scratched off. The presence circuit is much different and no negative feedback. It has all 12Ax7 preamp tubes except for the first tube with is a 5751. The output tubes are 6L6GC RCAs. Much everything else is the same. This one is a Little Jimi. I may ask the customer if he wants to change the reverb to be more like the other one. It is the same owner. I'm getting only about 356V plate voltage with the vintage 5AR4 in it. A new JJ GZ34 gets me to 395V and it sounds much better so I think the vintage tube is failing and I'll replace. Two of the pots were poorly grounded to the chassis like the other one but I just cleaned up the connection this time as it wasn't that bad. Probably not too many of these Holland amps in Hawaii!
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martin manning
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Re: Holland Amp

Post by martin manning »

Tweaking the reverb HF is an interesting idea. I've been wanting to try a reverb circuit with a tone control. You could try lifting one end of the snubber cap to see what effect it is having. Maybe try a smaller value or the other scheme with the cap from grid to cathode. Other differences (presence circuit, e.g.) may be what you are hearing.
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Darkbluemurder
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Re: Holland Amp

Post by Darkbluemurder »

This amp looks a lot like the Holland Brentwood I once had - reverb unit into Plexi circuit. That was a nice sounding amp.
I found the sweep control rather useless and converted it to a PPIMV.

Cheers Stephan
pula58
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Re: Holland Amp

Post by pula58 »

I worked on a Holland "Lil Jimi" several years ago. The pots weren't making good contact with the oxidized aluminum chassis! Same as you! So I roughed -up the metal and applied some non-ox pastes. What a difference it made!
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sonicmojo
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Re: Holland Amp

Post by sonicmojo »

I came across another defunct USA amp maker amp - a once Texas based Rhino amps Rhino Baby with 6V6s. I'm a sucker to save weird tube amps and I got this cheap. The preamp is not working correctly but the power amp section is working fine. With the preamp board out, it still can operate as a power amp. There is no information out there on this that I can find and I've decided that it is not worth debugging the original preamp. I'm planning to put in the Holland circuit that I previously documented and see how it turns out. The socket holes are not in a great spot but hopefully I won't make a big wiring mess. The cabinet is decent, ply or pine, with okay Eminence speaker. I'll post progress but need to order a few parts first.
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sonicmojo
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Re: Holland Amp

Post by sonicmojo »

I roughly drew up some layout changes and made a new eyelet board. I don't love the fact that the preamp tubes are between the board and controls but I think I minimized the crossing points and kept ground points opposite the power supply rail. Plus I should be able to run all cathode resistors/caps straight from sockets to board.

I ordered a few pots and a shorter reverb tank to fit the cab but I think I have everything else I need to complete it.
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